Freshwater ecosystems are home to an incredible diversity of species. Rivers, lakes, swamps, peatlands and all the other freshwater wetlands harbour more than 10% of the world's species. Each week, we will profile one of the most extraordinary.
#159 Short finned eel
Native to Australia, New Zealand and the South Pacific, the short-finned eel, Anguilla australis, have snake-like bodies and can reach up to 110 cm - They feed on crustaceans, molluscs, fish, aquatic insects and plants. They are thought to spend up to around 20 years in freshwater before they migrate to the sea to spawn - only once before death. After their larval stage, they are transparent, giving them the name “glass eel.” Under some circumstances, young eels can navigate cascades when migrating within their freshwater habitats, and on warm and damp nights they can travel short distances over moist ground - absorbing oxygen through their skin. An incredibly hardy species, they can endure long periods without food, burying themselves in the mud and entering an energy saving state when temperatures drop below 10 C. Short-finned eels are threatened by barriers to migration, habitat destruction, pollution and unsustainable exploitation. They are harvested and farmed on a global scale for consumption with an annual production of Anguillid eels estimated to be $US 1 billion. They are currently assessed as Near Threatened by the IUCN. However, there is no information regarding the population status of this species, and given harvesting and other risks, it is clear that more research is needed to determine distribution, harvest levels, abundance trends, as well as information on plausible threats.
#158 American Mink
The American mink, Neovison vison, is native to North America and can be found in a broad range of habitats including lakes, streams, rivers, swamps and marshes. It prefers densely vegetated areas and dens under stones or the roots of trees and self-dug burrows beside the water. They are fiercely territorial over their dens and are able to slip into narrow openings to pursue prey. American mink are nocturnal and feed on fish, crustaceans, rodents, birds and frogs. Strong swimmers, mink have partially webbed feet and a thick waterproof oily coat that allows them to stay in the water for long periods of time. When searching for food they are able to reach depths down to 30m deep! Mink are members of the mustelid family and are related to otters, weasels and badgers. They have also been seen climbing trees. They purr like a cat when they are happy and hiss and spray foul odour when they are threatened. They usually live alone and are only with their partners during mating season. Among the most valuable fur animals, they are commonly hunted for their fur. Most of the mink fur used in commerce is produced in farms. A negative outcome of the fur trade is that American mink have been introduced by humans outside their native range, including in Europe. The adaptations which mink successful predators in their native homelands of North America, can pose a serious threat to wildlife that did not evolve to live with them, and therefore they are considered a risk to native wildlife where they have been artificially introduced. In their native range American mink are an important part of the ecosystem, but habitat destruction such as alteration to vegetation along rivers and wetlands and water pollution threatens this species.
#157 Emperor Newt
Emperor newt, (Tylototriton shanjing), a.k.a. Mandarin newt or Mandarin salamander, is a rough-skinned newt found in the Gaoligong Mountains National Nature Reserve, Yunnan Province, China. Shanjing means mountain demon in Mandarin, referring to their highly toxic skin. This little demon’s orange spots on its back are actually poison glands, which will release toxins when attacked - containing enough toxin to kill 7,500 mice! Tetrodotoxin is the neurotoxin released from their skin that can be deadly to humans if ingested. The bright colours of the bumps on its back are said to resemble the jewels of the crowns of the emperor. Underwater, its spots can be mistaken for light reflecting off pebbles. They live in pools and slow-moving streams in subtropical forests at an altitude between 1,000 m to 2,500 metres above sea level. Generally nocturnal, they feed on earthworms, snails, centipedes and small invertebrates at night. Females are larger than males and during mating, they circle each other underwater with their snouts touching. The female deposits eggs on rocks and plants in standing water bodies. The major threat is over-collecting for traditional medicine. Small numbers are ending up in the pet trade, and its habitats have been lost and are threatened by further development for human settlement. Defined as Vulnerable by the IUCN.
#156 Common Pipewort
Found in the shallow water of lakes, ponds, marshes, wetlands and slow moving rivers, the Common Pipewort, Eriocaulon aquaticum, a.k.a the seven angle pipewort has blooms of tiny flowers held up above the water line attracting pollinating insects. While many aquatic plants are wind or water pollinated, pipeworts have a nectar gland at the tip of each petal to attract pollinators. Widespread across North America and Canada, pipeworts have a tall leafless stem with a button-like white flower. The part of the plant submerged underwater provides a habitat for invertebrates, which are in turn a food source for aquatic species. Beetles also feed on the roots and shoots. Their height depends on the water depth it is growing in - up to several feet high! Pipeworts improve water quality by transporting oxygen to its underwater roots, stems and leaves. This oxygen leaks into surrounding spaces where microorganisms decompose organic wastes, very similar to a water treatment plant. Populations of pipeworts have declined globally, mainly threatened by shoreline development and pollution.
#155 Freshwater Blenny
The freshwater blenny, Salaris fluviatilis, is found in Morocco and Algeria, widespread across Europe and is also found in Turkey and Israel. As a bottom-dwelling fish species it likes gravel and rubble substrate with moderate to high current velocity. Populations are generally small and highly localised. Generally reclusive, they protect themselves from predators using their brown mottled skin that blends in with the rocks. Males make nests under large stones where they attract females for spawning. The females lay the eggs and the male guards them against predators until they hatch. Threats to this species include eutrophication, gravel extraction and habitat destruction. In addition, dams and the channelization of rivers have fragmented rivers and water extraction and drought may hamper reproduction. Life-history traits of the freshwater blenny suggest that it may be vulnerable to more severe drought conditions. In five of the nine Mediterranean countries they are classified as vulnerable or endangered. The removal of gravel and stones from rivers for the construction industry threatens the freshwater blenny due to their very specific nesting requirements. Water pollution, especially from urban wastewater and the introduction of non-native species also threaten the freshwater blenny.
#154 Red Line Dwarf Cichlid
Native to the Orinoco Basin in South America, the Red Line Dwarf Cichlid Dwarf, Apistogramma hongsloi, typically live in small slow-moving streams. Known as Viejita in Colombia, this colourful dwarf cichlid can be found in many streams of the Orinoco River basin, especially the ones between the Sipapo and Cuchivero Rivers. Part of its distribution lies in El Tuparro National Park in Colombia and in the RAMSAR protected wetland of the Bita River. Males have red markings distinguishing them from other Apistogramma species. In the breeding periods, males spend much of their time flashing their fins at each other and displaying brilliant colours. In the sunny sections, the river banks are heavily planted and the light-coloured sand is covered in periphyton. These sunny spots are where you can find many Red Line Dwarf Cichlids gulping up the sand, sifting through it, and spitting out the inedible matter. Females maintain their distance and are usually more inconspicuous, hiding under leaf litter or between the aquatic plants. Sexually dimorphic, males and females differ in colour and the males are larger than females. Highly sought after by aquarists, this species is found in people’s aquariums around the world. There is no estimated population size of this species, however it faces a number of threats including habitat loss, water pollution and overharvesting. There is a need to understand the population size, distribution and trends to better protect this species.
#153 Bakara Sulawesi elephant snail
The Bakara Sulawesi elephant snails, Tylomelania bakara, are endemic to Sulawesi, Indonesia. They are often referred to as rabbit snails due to their drooping antennas resembling long rabbit ears. Most of them occur in the ‘ancient lakes’ of Sulawesi in the region of Tanjung Bakara in Lake Towuti. A rock dwelling freshwater lake species, they can be found at a depth between 2-20m in 27-30℃ feeding on algae. Recognized by their distinct shell shape, they can grow as long as a man’s finger. Studies have found that they have originated as far back as 5.4 million years ago. Bakara Sulawesi elephant snails lay eggs every 4-6 weeks with each egg sack containing 1-2 baby snails. Like most snail species, they become immobile and hide in their shell when they sense danger. They are threatened by nickel mining and hydropower dam installations which impact natural water fluctuations in the lake. Many species of Tylomelania are collected for the aquarium pet trade. Harvesting could cause a very rapid decline of this species due to its already very limited distribution. They are currently listed as Critically Endangered by the IUCN Red List of Threatened SpeciesTM based on its extremely limited distribution and continuing deterioration of habitats. A major project initiated by Shoal Conservation to establish a management and action with local governments, communities and the private sector to protect the ancient lakes of Sulawesi is underway aiming to highlight key areas for conservation.
#152 Common Carp
The Common Carp, Cyprinus carpio, is a widespread freshwater fish species native to eastern Europe and central Asia in the rivers that drain into the Black, Caspian and Aral Seas, but has been introduced into freshwater habitats around the world for food and sport fishing. Common carp found in the Danube River 2000 years ago were kept in specially built ponds by the Romans for consumption. At the same time, it was the first fish species domesticated in China. Both European and Asian subspecies have been farmed and spread by monks between the 13th and 16th centuries. The Common Carp is one of the major species produced in world aquaculture. Worldwide more than four million tons of common carp are produced annually in aquaculture - making them one of the most economically important fish species. Carps are one of the four species that account for 85% of total inland water catches. Although gregarious (one fish can lay over a million eggs in a year) common carp populations have declined by 30% in their native range due to river habitat modification including channelisation which removes in-river habitat and disconnects river from their floodplains, and the installation of dams, which literally cut rivers in half. As Common Carp are naturally potadromous (migrate within rivers to complete their life cycle) and require flood plain areas to spawn, river modifications are a significant threat. Furthermore, hybridisation with farmed fish is a threat to this species. They are defined as Vulnerable by the IUCN Red List of Threatened SpeciesTM.
#151 Common Yabby
The Common Yabby, Cherax destructor, is a crayfish species endemic to Australia and found as far south as Tasmania. The word Yabby comes from the Wemba Wemba Australian aboriginal language. The most widespread species of freshwater crayfish, the Common Yabby, is found in swamps, dams, streams and rivers. As all crustaceans, they have no skeleton but a hard exterior shell known as an exoskeleton. Opportunistic feeders, they are omnivorous - feasting on just about anything including themselves - cannibalistic when insufficient food is available. They can grow up to 30 cm long and their colour varies based on which season they are found, and can also vary from individual to individual found in the same location. Most commonly found in a drab olive, dun or light brown colour, they have also been found to range from black, ochre-yellow and brown to red and blue. Yabbies grow by moulting, shedding of their shell - they will take up water and store it within their body tissues to expand their new shell. The Common Yabby can survive in temperatures ranging from 1C to 35C. They can dig burrows down to 50 cm deep - allowing them access to water in the shafts during dry spells in the summer. Found in areas where oxygen levels are high and there is plenty of vegetation. Listed as Vulnerable by the IUCN Red List of Species ™.
#150 Hawaiian freshwater goby
The O’Opu or Hawaiian freshwater goby, Lentipes concolor, can’t move mountains, but they sure can climb them! More accurately, they can climb the waterfalls of mountain streams of Hawaii, where they are endemic. They use suction disks on their ventral sides formed by the fusion of pelvic fins to climb the wet rocks behind waterfalls, even scaling the 135 m Akaka Falls. Studies show that the O’Opu can reach fast flowing upper stream segments and the elevated suction pressure enhances its ability to successfully capture food. They also need these continuously flowing streams for critical reproductive periods - they are amphidromous, meaning their life cycle is split between freshwater and marine environments, which has enabled them to avoid the inevitable extinction that would befall landlocked fishes in streams destroyed by volcanism or erosion. Adults live in freshwater, where they spawn, and once the larvae hatch, they are washed into the ocean to feed. After metamorphosis, juveniles migrate back to the streams to live the rest of their adult life. Males have black heads and orange tails, while females an olive to brown colour. But both have bright blue eyes. Culturally important, the Hawaiian freshwater goby is food fish for Hawaiians. They were cultivated in aquaculture in the 16th century and aided in the production of the root vegetable, Taro by pruning the leaves and removing pests- a win-win for aquaculture and agriculture. As a narrow-range endemic species, with a unique life cycle, like other pacific island gobies, the Hawaiian freshwater goby is particularly sensitive to anthropogenic changes that may disrupt stream flows, such as channelisation, dams, and water diversions. Assessed as Data Deficient by IUCN Red List, this intriguing species urgently needs more study.
#149 Dog faced water snake
The dog faced water snake, Cerberus rynchops, also known as the bockadam snake is native to South and Southeast Asia. Found in mangrove forests, mudflats, tidal creeks, estuaries and rivers, they have flattened tails and very small strongly keeled scales that help them to swim better. Their valvular nostrils create a watertight seal that allows them to live underwater without inhaling or drinking too much water. They have salt secreting glands enabling them to distil the water they take in. Well camouflaged, the dog faced water snake blends in well with mud and litter. The name dog faced water snake is due to their large head and snout. Once born, they are independent from their parents. They are rear fanged and mildly venomous. Dog faced snakes have been seen jumping across mudflats using a sidewinding technique.They are nocturnal, feeding at night mainly on small fish, crustaceans and frogs. They hunt in shallow water and often hide under the mud. They were historically traded and used for their skin in the Philippines. While this is no longer the case in the Philippines, it is possible that they are still collected for the leather trade in some countries. Known for their bright orange and yellow bellies which mostly occurs in females. Its eyes are located at the top of their heads, allowing them to see while half-submerged and hidden in the mud while still watching for prey or predators. Although assessed as Least Concern by the IUCN Red List of Species ™, the species has localised threats, in particular in its preferred mangrove habitats.
#148 White-tailed Eagle
Appearing in Germany’s coat of arms, the White-tailed Eagle, Haliaeetus albicilla, has one of the largest wingspan of any eagle in the world - up to 2.5m! Living most of the year near large bodies of water, the White-tailed Eagle can be found both on coastlines and inland freshwater areas. Found across Eurasia as far west as Greenland and as far east as Japan, the white-tailed eagle has strongholds in Norway and Russia. Spending most of their day perched on trees, they require forested areas and access to lakes, wetlands, rivers and marshes. Opportunistic feeders, they snatch food from birds and otters but they are also excellent fishers, taking fish at the surface of the water, where they can reach speeds of up to 70 km/hr. Nests (known as ‘eyries’) are built from mature trees, branches and twigs and can be up to 2m wide. Females lay 1-3 eggs, and for the first three weeks after hatching, males do all of the hunting. Their offspring leave after 70 days but they are dependent on their parents for 5-6 more weeks. Destruction of wetlands and poisoning from pesticides threaten the white-tailed eagle. Conservation measures such as protecting eyries, providing safe food and re-introduction into specific areas have been put into place. In addition, conservation actions such as adaptive management of wind farms (turning them off during migration periods), preserving perch trees and encouraging use of lead-free ammunition in hunting should be put into place to safeguard this species.
#147 Freshwater Crab
Found in lakes, rivers and streams throughout Southern Europe, the freshwater crab, Potamon fluviatile, only resides in freshwater areas. Feeding at night either in the water or on land, they are aggressive using their right claw to attack, the majority being right-handed. Young crabs are more aquatic than adults. An omnivorous species, they feed on worms, insects, shrimps, small fish, amphibians and algae. They hide under stones and vegetation for shelter as well as dig burrows under banks - up to 80 cm deep! From November to February, they hibernate in burrows or natural refuges. Females are generally smaller than males and individuals can live up to 12 years. They have very few predators - their main threat being humans - individuals catching 3,000-10,000 per season. Threatened by pollution, habitat degradation and over harvesting, these European freshwater crabs are listed as Near Threatened by the IUCN. The survival of these crabs relies heavily on habitat protection and preservation of freshwater ecosystems as they use burrows and vegetation to seek refuge from predators. With the Convention on Biological Diversity (CBD) COP coming up next week, it is critical that leaders recognise the importance of safeguarding freshwater biodiversity.
#146 American Paddlefish
Living fossils, American paddlefish, Polyodon spathula, date back to 125 million years ago and are found from the Mississippi basin to New York to Montana and South to the Gulf of Mexico. A species of ray-finned fish closely related to the sturgeon, paddlefish are also harvested for their meat and caviar as an alternative to sturgeon. As filter-feeders, their constant grazing on tiny aquatic organisms helps keep their populations in check with zooplankton as their primary food source. Its snout extends 1/3 of its body length - which is covered with thousands of electroreceptors to locate zooplankton and facilitate migratory behaviour. With undeveloped eyes, they also rely on these electrical receptors for navigation. American paddlefish can grow up to 2 metres long and weigh up to 90kg! Requiring open, free flowing rivers, paddlefish populations have declined due to stream channelisation, levee construction and drainage of bottomlands. Dams prevent paddlefish from being able to move upstream to their spawning territory. The American paddlefish is the only living relative of the Chinese paddlefish, which has recently been declared Extinct by IUCN. Paddlefish populations have declined due to overfishing, pollution, barriers to migration and habitat destruction and are listed as Vulnerable by the IUCN. The American paddlefish is the only member of its family left on Earth. Control of sport and commercial fishing through federal regulations have helped bring back populations and other conservation measures that increase fish passage are being considered.
#145 Asian small clawed otter
The smallest otter species in the world, the Asian small clawed otter, Amblonyx cinereus, hardly reach 5 kg and are found in South and Southeast Asia. Asian small clawed otters are playful, social animals forming small family groups. Very adaptable, they are found in mangrove & peat forests, swamps, fast flowing and stagnant waters. They require plenty of vegetation for protection and shade. They are also found in rice paddy fields feeding on crabs which is seen as an asset to rice farmers as crabs are pests to their rice paddy fields. They are excellent swimmers, they start swimming at 3 months old by using their back legs and tails. They have two layers of fur with the outer layer being waterproof. Air gets trapped between their two layers of fur which keeps them buoyant in the water. After swimming, they rub up against logs and vegetation to mark their scent - individuals have distinct scents as humans do with fingerprints! Massive destruction of wetland forests across their range, including in Indonesia, and conversion into palm oil plantations in Sabah, has resulted in significant habitat loss for this species. Threatened by habitat loss, pollution and hunting, the Asian small clawed otter is listed as Vulnerable by the IUCN. Protecting and restoring resilience across entire river basins including their deltas is crucial in mitigating biodiversity loss. Find out more about our resilient asian deltas initiative in the freshwater practice and what we are doing to protect and restore Asian deltas.
#144 European River Lamprey
The ancient migratory freshwater species, the European river lamprey, Lampetra fluviatilis, come from the lamprey family which were the first fish to evolve 530 million years ago. European river lampreys are jawless fish, characterised by a funnel-like sucking mouth with teeth - boring into the flesh of other fish and feeding on bodily fluids. Resembling eels, they have a strong flexible cartilage instead of bone and have an average length of 30 cm. Their reproductive cycle is similar to a salmon, hatching in rivers, going to the sea to feed and migrating back into rivers for spawning from autumn to spring. Adults die after spawning -laying up to 25,000 eggs! The larvae spend several years in soft sediment before migrating back to the sea. The construction of dams has reduced their numbers as they are unable to move upstream to their spawning grounds. Worldwide rivers have been fragmented by dams and other hydraulic structures contributing to freshwater biodiversity loss. River lampreys are poor swimmers, thus, not well-adapted to pass barriers. In almost every watershed, lamprey habitats are fragmented. Maintaining connectivity between freshwater spawning and rearing habitats and estuarine/ocean feeding areas is crucial for river lamprey species. In Spain, the river lamprey has been declared officially extinct since 2018. Find out more about dam removal projects in the EU to protect freshwater migratory species like the river lamprey. Allowing free flowing rivers is essential to preventing biodiversity loss in our freshwater ecosystems.
#143 Nile Monitor
The second largest reptile found in the Nile, the Nile Monitor, Varanus niloticus, can weigh up to 20 kg. Highly adaptable creatures, they can be found along the Nile in sub-Saharan Africa in forest, savanna, woodland, bushland, varied aquatic habitats from mangroves to lakes and rivers. Highly aquatic, Nile monitors thrive around rivers and lakes, they spend most of their time in the water - with the ability to remain underwater for up to 15 minutes! They are strong, active swimmers and when they sense danger, they can be seen leaping from tree branches into the water. Nile monitors are known for their muscular bodies, strong legs, powerful jaws and muscular tails shaped like rudders that aid them with swimming. During the day, they can be seen basking on the shoreline and at night they are found sleeping in burrows, submerged in water or on tree branches. Generally solitary animals, Nile monitors rarely interact with each other outside breeding season where males and females mate with multiple partners. Nile monitors are important predators, controlling populations of various prey species such as crocodiles as they feed on crocodile eggs. The main threats to Nile monitors are the pet trade and hunting for food, leather and traditional medicine.
#142 Magdalena Turtle
The prehistoric-looking freshwater turtle known as the Magdalena river turtle or Podocnemis lewyana, is endemic to Colombia, distinct to the Magdalena and Sinu Rivers, but also found in the San Jorge and Cauca River. They diverged from other turtles over 100 million years ago - around the same time humans shared a common ancestor with bats & tigers! Among freshwater turtles they have some of the longest aquatic migratory patterns rarely leaving the water except to bask. Primarily found along the banks of rivers, they are also found in flooded areas connected to rivers where they spend their time basking in the sun. Nesting occurs twice a year during low water level periods on gravel or sand beaches as well as banks and pastures when river levels are low - laying an average of 22 eggs. Adult females are larger than males, weighing up to 8kg and 500mm in length. Locals see these turtles as a source of protein and believe that consuming them provides medicinal benefits such as curing diseases and recovering from pregnancy. Magdalena river turtles are threatened by habitat destruction and pollution, hydrological changes due to dams, traditional consumption and commercial exploitation. The consumption of turtle meat during Lent is deeply rooted in northwestern Colombia’s culture - with over a million turtles thought to be consumed during this period! Populations have declined over 80% in the last 25 years, listed as Critically Endangered by the IUCN. Exploitation of the Magdalena river turtle is prohibited in Colombia, however it is often unenforced.
#141 Proboscis monkey
The Proboscis monkey, Nasalis larvatus, resides in mangrove, peat swamp and freshwater swamp forests - rarely straying away from water. They are known for their unusual appearance with diverse colour patterns of orange, yellow and pink and are distinguished by their long noses - up to 17 cm long! Their noses help them produce loud bellowing sounds to raise alarm and attract females. They are endemic to the island of Borneo, where is distributed on both the Malaysian and Indonesian sides of the island, including in rivers such as the Kinabatangan and Mahakam. Among primates, Proboscis monkeys are the primate world’s most prolific swimmers - seen frequently swimming across rivers and distances of up to 20m underwater. They have evolved webbed feet and hands, allowing them to outrun crocodiles at times. Proboscis monkeys leap into the water, doing one of their comical belly flops, and are able to take deep dives when they feel threatened. Highly social animals, they form troops of 2-30 with a male leader and can be seen together resting and sleeping on mangroves at the edge of the water. In order to get enough energy, they have to eat large amounts of leaves and unripe fruits which enlarge their stomachs - giving them their pot bellies. Due to hunting and habitat destruction, Proboscis monkey populations have declined drastically. Populations have declined by 70% over the last 36 years. The infamous Borneo forest fires and clearing of forests for palm oil plantations have been major contributors to their decline. They are listed as Endangered by the IUCN. They are currently protected in Borneo.
#140 Pygmy Hippo
The Pygmy hippopotamus, Choeropsis liberiensis, are the smallest species of the hippo family that are reclusive and nocturnal. They are half the size of and weigh ten times less than the Common Hippo. They rely on freshwater to keep their skin moist and their temperature cool. Pygmy hippos are solitary animals - only when a female is accompanied by their young or briefly during breeding are they seen as a pair. They spend roughly 6 hours a day feeding on terrestrial and semi-aquatic plants and spend the day hidden in swamps, wallows and hollows under the banks of streams. Pygmy hippos follow well-defined trails which they mark by vigorously wagging their tail while defecating. Their closest living relatives are whales and dolphins and hippopotamus is derived from the Greek word “river horse”, as it spends its time in rivers and swamps, with its nose and ears close underwater. Featured in folktales, Pygmy hippos find their way through the forest by carrying a diamond in its mouth to light up its path and they must be caught at night to take the diamond. Deforestation due to palm oil plantations, cultivation and mining and logging, has destroyed their habitat. In addition to habitat loss, increasing hunting intensity has threatened the Pygmy Hippo populations - with only a few thousand left in the wild. They are listed as Endangered by the IUCN. Remaining Pygmy Hippo populations are fully protected in all state range countries and are mainly found in protected areas.
#139 African Bullfrog
The African Bullfrog, is also known as the Pixie frog due to its scientific name, Pyxicephalus adspersus. It is among the largest of the frogs on the planet, with males weighing up to 1.4 kilos and measuring up to 24.5 cm in length - the size of a dinner plate! Females are half the size of males, which is unusual as female amphibians are generally larger. Found widely in South Africa, Swaziland, Namibia, Botswana, and Zimbabwe, they also extend north to southern Angola, Zambia, Malawi, Mozambique, Tanzania, and Kenya. They are also one of the most adaptable amphibians on Earth - able to survive the harshest African environments. When living in areas that are completely dry for years, with temperatures ranging from 0 - 40 ℃, African Bullfrogs burrow underground, forming a tough cocoon called an estivation chamber. They are only active during the rainy season, waiting it out for six to ten months - spending most of their lives estivating underground. As carnivores, their diet consists of small rodents, small birds, reptiles, invertebrates and insects. But they are also a cannibalistic species - male African Bullfrogs are known for eating their own tadpoles, which they guard. During breeding season males congregate in large groups displaying aggressive behaviour such as pushing, biting and even consuming smaller males. Large males push their way to the centre to begin their mating call and females dive towards the dominant males. Once fertilised, females release as many as 4,000 eggs! African Bullfrogs are harvested for local consumption and caught for the commercial pet trade. Some populations are declining in South Africa due to loss of their breeding habitats.
#138 Granular Salamander
Found in subtropical and tropical high-altitude grasslands, freshwater marshes and ponds, the granular salamander, Ambystoma granulosum is a species of mole salamander only found in a small area of central Mexico close to Toluca in Mexico State - 3000 metres above sea level. Mole salamanders diverged from all other salamanders in the Late Jurassic period - over 150 million years ago! These amphibians live around 5 years and breed in marshes, dams and small ponds. They are a metamorphosing species giving them the advantage of reproducing in aquatic environments, swapping out their gills and fins present in their larval stage for eyelids and lungs in their adult stage. Thus, spending the majority of their lifetime on land in grasslands and returning to freshwater to breed yearly and feed. They are threatened by habitat loss, pollution and overcropping due to forest clearance and water extraction by extensive urban and agricultural expansion. Due to low food availability, Granular salamanders experience high mortality rates in their early life stages. Non-native predatory fish are also a major threat to these salamanders. The granular salamander is classified by the IUCN as Endangered as the species has declined over 50% in the last 25 years. Conservation and restoration of the Granular Salamander's habitat is urgently needed.
#137 Tisza Mayfly
Flying over the Tisza River, Tisza mayflies are aquatic insects named after this transboundary river that flows through Hungary & Serbia where it meets the Danube. Tisza mayflies, Palingenia longicauda, are also known as the Long-tailed mayfly and Giant mayfly because they are the largest of the mayfly species, measuring 12 cm from head to tail. Never moving away from water, they fly low, often touching the surface of the water. “Blooming of Tisza” has become a tourist attraction during a week in June, where Tisza mayfly larvae hatch. The spectacular synchronised swarming of millions of these aquatic insects can be seen just above the water’s surface, frantically trying to mate after hatching as they only have a few hours to mate before they die. The Tisza mayfly has become a symbol of freshwater conservation efforts in Central Europe, especially in Hungary - their presence is a sign of clear unpolluted water, promoting healthy rivers. This species used to be widespread in medium-large rivers throughout Europe but have experienced 98% range loss in the past century. The Tisza mayfly has dramatically declined due to rapid, intensive hydromorphological alteration and pollution of European rivers that peaked around 1930. It’s now extinct from the Loire (France), the Rhine (Germany), and the Danube (Serbia and Bulgaria). Conservation efforts are underway to protect these aquatic insects in their native habitats in Hungary as well as repopulating the Rhine in Germany.
#136 Spangled Perch
As Australia’s most widespread native freshwater fish, the Spangled Perch a.k.a the Spangled Grunter or Jewel Perch, can grow up to 25 cm in length. Leiopotherapon unicolor is naturally found in the freshwater systems in Northern Australia such as the Murchison River, Hunter River, Murray-Darling system as well as the Lake Eyre/Bulloo-Bancania Drainage System. They like swimming in a wide range of waters with little vegetation such as rivers, lakes, dams, billabongs, bore drains, wells and waterholes. This hardy species can survive severe dry periods, found in wet sand after surface water has dried up. It can also tolerate a wide range of temperatures and salinity levels. The spangled perch has a high dispersal rate and the ability to colonise less accessible habitats quickly. Labelled as an extreme dispersal species, this species moves up to 300 km after a flooding event. Females spawn 24,000 to 113,000 eggs allowing their populations to multiply quickly. As opportunistic feeders, the spangled perch have a diverse range of prey including small aquatic insects, fish, molluscs (eg. water snails), crustaceans (eg. shrimps) and plant matter. They are highly adaptable to new environments and can attack a wide range of native aquatic life. Spangled perch can potentially have a highly destructive impact on native species if introduced into waters outside of their range. The Spangled Perch is listed as Least Concern by the IUCN.
#135 Spotted-necked otter
Spotted-necked otters, Lutra maculicollis, are known for their namesake and distinctive spots around their neck and upper lip. They are one of the four mammal species native to Africa's Mara River and throughout sub-Saharan countries from Guinea Bissau to southwest Ethiopia and southeastern South Africa. As cubs, they are very dependent and may stay with their mother for up to two years. While typically solitary, for a portion of the year spotted-necked otters live in small family groups and enjoy playing with each other. Social life provides some advantages: foraging in loosely-knit groups of around 20 allows them to catch prey - frogs, crabs, small water birds, and especially fish - easier. They are considered the most aquatic African otter, as they are well adapted to their freshwater environment, rarely moving more than 10 m away from water. They require permanent water sources with high fish densities, which they catch with their sharp claws while swimming with fully webbed paws. Able to dive down to depths of 14 m, they can spend 4-6 hours underwater daily. Because they are diurnal and mainly hunt by sight, they need clear unpolluted water. Vegetative cover such as long reeds, bushes, and grass along the shoreline are also essential to provide cover for resting and denning. Listed as Near Threatened by the IUCN, they face threats such as habitat loss, fishing conflicts, fish nets, and poaching. Non-native species like the Nile perch are a potential threat to the Spotted-necked otter because they push the smaller local species to the brink of extinction, threatening their food supply.
#134 AMAZON LEAFFISH
Leaf or a fish? When swimming in the waters of the Amazon and Orinoco river basins, it might be challenging to determine which one it is - an advantage for this small fish. The Amazon leaffish, Monocirrhus polyacanthus, might seem harmless but is a "wolf in sheep's clothing" or, better yet, a "fish in leaf's clothing". Their remarkably laterally compressed body and orange-yellow to brown colours resemble a floating dead leaf, making it easier to approach unaware prey. The colour patterns' mimicry is outstanding, with several markings that give the impression of dry leaves. But they don't rely only on appearance, putting up a whole show - they actually mimic their environment to facilitate their attack. Amazon leaffish are known to prefer oxbow lakes and streams of blackwater rivers, which are typically dark due to plants' decomposition. Adults live in shallow waters, near fallen leaves on the surface, swimming in a floaty manner towards their prey - fish, crustaceans, and insects. Some scientists say their coloration can adapt to the environment and accentuates during reproductive periods. Sadly, not much more is known about this ludicrous fish. Reproduction has only been observed in aquariums, where it showed an aggressive courtship and male parental care of eggs and larvae, while the female is responsible for driving away intruders. Due to its curious-looking body and rarity, it's exploited by the ornamental fish trade.
#133 European crayfish
Also known as Noble crayfish, the European crayfish, Astacus astacus, is indigenous and widespread throughout its namesake continent. But it's the only native freshwater crayfish species in Norway and Sweden. It has been traditionally fished and eaten for centuries in the latter country, having considerable cultural, social, and economic value. From large lakes to small streams, it prefers shores and shallow waters, especially where it can hide from predators (e.g., minks, otters, and eels) like steep banks where it digs deep burrows. They are nocturnal and omnivorous. When the water starts to get cold in Autumn, it's mating time. Females carry the fertilised eggs under their back until the following summer when the eggs hatch with tiny crayfish. These younglings can grow up to 18cm and live a long time, likely over 20 years. But some might not make it, as their populations have decreased dramatically locally. This species is Critically Endangered according to the Swedish Artdatabank's National Red List 2020, mainly due to an invasive species - the Signal crayfish. During the 1960s, introductions in Swedish waters aimed to replace the native species affected by crayfish plague. But it was not known that the North American crayfish carried the plague while withstanding the disease. The European crayfish also faces habitat loss and degradation, as their natural river flows are being altered by hydropower dams. But there's still hope. It's listed in the EU's Species and Habitats Directive, which means that Sweden has a national responsibility to manage the stock. WWF's conservation work focuses on their freshwater ecosystems' health.
#132 Goliath frog
Meet the world's largest frog – the Goliath frog, Conraua goliath. Also known as Giant slippery frog, it can reach the size of a small cat – up to 34 cm long and over 3kg. Native to a narrow rainforest region of Cameroon and Equatorial Guinea, it lives in or near clean, large, and fast-flowing rivers and streams. This river giant is omnivorous and opportunistic, feeding both submerged or out of the water. Although scientists previously thought it didn't vocalise, it has an interesting repertoire of calls that includes short whistles, chirping, and even a "sighing deep roar". During breeding, they create nests in streams and small rivers by clearing the area of residues and leaf litter. Recently, scientists found that nesting (likely done by males) includes the heavy lifting of rocks up to 2kg – which might explain why this species evolved such a large body. They observed 3 types of nesting sites to protect developing offspring from river torrents and predators: rock pools, existing washouts, and dug-out depressions in gravel riverbanks. Adults guard the nests filled with 150-300 eggs at night, where tadpoles finish their development into frogs. When feeling threatened, they escape by jumping into the water with a single leap, sometimes skittering across the surface with consecutive hops reaching 3.5m. On land, they seem exhausted after a few jumps, making them easy to capture. Listed as Endangered, they face threats like overhunting for food and the pet trade, habitat and sedimentation loss due to agriculture and hydropower dams, and climate change. Conservation efforts should include keeping their rivers healthy and flowing and working with the local communities to manage harvests sustainably.
#131 Genji-botaru firefly
Few insects get such a high level of people's attention as fireflies do. And the Genji-botaru firefly, Luciola cruciata, probably like no other in Japan. Of 2000 firefly species worldwide, fewer than ten are aquatic at the larva stage. Distributed throughout Japan's main islands (Honshu, Shikoku, and Kyushu), Genji-botaru's larvae live in clean fast-flowing rivers, streams, and rice paddies, and all its stages - eggs, larvae, and pupae, adult - are luminous. Aquatic fireflies have been very popular in Japan since ancient times, when people lived in a suburb-like environment cultivating paddy rice with water from nearby streams and often saw the tiny bright lights. They believed the fireflies' lights were the dead's souls. This human-fireflies connection is evident in Japanese literature, where they were depicted as essential items; in art, drawn in old woodblock pictures and painted on refined porcelains; and in traditional children's songs, like the "Hotaru Koi" (= Come, fireflies). During summer, a typical evening activity was "Hotaru-gari" (=firefly hunting). Signalling a seasonal change, at its peak, people would take boats to find the best places to see one of the most spectacular events involving luminescent animals to this date – a large number of flying males flashing in synchrony to attract females. Females lay their eggs among the riverbanks' moss, and after they hatch, larvae crawl to the water, where they spend months underwater feeding on freshwater snails. Once young fireflies, they go back to the riverbank and become adults. Slowly and silently, they start shining their light and hover over the river when it's time to court. Sadly, this brilliant species is at risk. Its wild population decreased dramatically in the last ten years due to pollution, habitat loss, and commercial capture. Conservation efforts include Genji-botaru's repopulation activities and the designation of several areas – especially those where these fireflies swarm - as natural monuments by the Japanese government.
#130 Yellow-spotted river turtle
Native to several South American countries, the Yellow-spotted river turtle, Podocnemis unifilis, is one of the largest freshwater turtles. This species is called charapa or side-necked turtle as it cannot completely insert its head into the shell but bend its neck to one side to attach, leaving a part open. It’s known to inhabit the colossal Amazon River basin, preferring the main channels of large rivers, where it spends most of its time underwater. Yellow-spotted river turtles’ reproductive behaviour is synchronised with seasonal variations in water levels – every year, they congregate for mating and spawning in the dry seasons. To prevent nests from being washed away, they lay their eggs on the dry rivers’ banks and sandy beaches. And hatching mostly coincides with the beginning of the rainy season. They feed on small animals (e.g., crustaceans, insects, molluscs, and fish) and aquatic plants and fruits, being critical seeds disperser. In addition, they have another crucial ecological role as a food source for other animals, including humans. Harvested since pre-colonization times due to its high nutritional value, it is nowadays mainly threatened by unsustainable exploitation, followed by habitat loss and degradation, and climate change. In Ecuador, their populations have declined so severely due to illegal commercialization and overharvesting that they are listed as Critically Endangered. But there is hope - ongoing projects with indigenous communities in the region are looking to restore the Yellow-spotted river turtle populations. Conservation efforts for this and other Amazonian freshwater turtles are likely to be more successful with local community involvement, healthy freshwater habitats, and free-flowing rivers.
#129 Baltic Sturgeon
The Baltic sturgeon was integral to the region's fauna and culture until the middle of the 20th century. Although it spends most of its long life – up to 150 years – in marine waters, the Baltic sturgeon, like all migratory fish, is vulnerable to diverse habitat impacts because they use rivers, estuaries, bays, and the ocean at various points of their life. Their spawning sites include the Baltic Sea's southern tributaries, like the Oder river, ranging from lower sections to headwaters around 1,000 km from the sea. But they were overfished, their migratory routes blocked by hydropower dams, and their habitats polluted – subsequently, the population disappeared with the last documented sighting in the Baltic Sea in 1996. After several years of debates, genetic investigations have shown that the closest remaining relatives come from the northernmost populations of Acipenser oxyrinchus in North America. These populations support restocking efforts in the Baltic Sea range, and results show increasing numbers of juveniles in coastal waters. Yet, there is still no evidence of returns of mature fish or natural reproductions. The year 2022 marks the 15th anniversary of restocking events in the Oder River, where several million fingerlings have been continuously released in cooperation between Germany and Poland. As the species needs approximately 15 years to mature, hopes are high that we can soon witness their first natural reproduction. However, these efforts will only be truly successful if we tackle why they were extinct in the first place. Fisheries with bottom-set gillnets pose a huge threat to the Baltic sturgeon, which ends up as by-catch. But the most pressing threat comes from the navigation development projects in the Oder river basin. Poland and Czech Republic governments plan to create the E30 Waterway, which would basically turn the river into a channel and destroy river banks or deep holes, which are used by sturgeon to overwinter and reproduce. This infrastructure would also be detrimental to a wide range of aquatic biodiversity and completely alter the Oder. But we can still save the Oder and its wildlife. In addition to restocking, sturgeons' conservation efforts include habitat restoration, raising public awareness and political will to support implementation, advocating for alternative renewable energy sources, and removing old dams.
#128 Ship sturgeon
The Ship sturgeon, Acipenser nudiventris, is extinct in the Danube and thus the entire EU territory, despite being protected under the EU Habitats Directive. A sad event that has, since its adoption in 1992, rarely happened before. On a global level, this species' population declined more than 99% in the past three generations (around 120 years). Nowadays, the only confirmed self-sustaining population results from a translocation out of the native range within Kazakhstan. Like the majority (2/3) of sturgeon species, it is listed as Critically Endangered by the IUCN Red List of Threatened Species, indicating its high risk of extinction. Sturgeon are the world's most threatened group species due to historic overexploitation. They face ongoing poaching for illegal trade in wild caviar and meat, hydropower dams blocking migratory routes, unsustainable sand and gravel mining, and habitat loss. As migratory fish, they are good indicators for connected ecosystems - their disappearance highlights freshwater biodiversity's decline and our rivers' degradation. Ship sturgeons used to swim the Black, Aral, and Caspian Sea basins, including large rivers like the Danube. Although there are pure freshwater forms of ship sturgeons, like many sturgeon species, they spend part of their life in salt water and return to rivers to breed. It could reach 2,2m in length, weigh up to 120kg, and live for more than 30 years. The situation for ship sturgeon is bleak. But there's still hope, especially after scientists found six young ship sturgeon in the Rioni River, where a recent expansion of a sturgeon-protected area could boost conservation efforts. WWF's Sturgeon initiative is also working to restore our rivers' health and give sturgeons a fighting chance.
#127 Rough-skinned newt
The Rough-skinned newt, Taricha granulosa, is a stocky salamander known for its annual mass migrations and potent toxin. Endemic to the hilly and mountainous forest areas of the USA and Canada Pacific Northwest, this species can be found on land or in ponds, lakes, reservoirs, and slow-moving streams. They migrate to and from these aquatic habitats, where they find a mate and breed (check this fantastic video). After fertilisation, the female deposits the eggs singly from her cloaca on aquatic plants, submerged twigs, and detritus. Rough-skinned newt’s larva preys on small aquatic invertebrates, and some populations develop into gilled adults, but they mostly breathe through lungs and their skin when swimming. Even though it carries a cute-looking face and a small body for humans - up to 22 cm in length - it’s the most toxic newt in North America. Its toxin, known as tetrodotoxin, is harmful to people and responsible for severe illness and even death when ingested – it’s crucial to be careful and avoid touching them. The toxin serves as an antipredator defence, but they are still prey to racoons and especially garter snakes, which evolved resistance to it. Rough-skinned newts also have another strategy: when feeling threatened, they adopt a defensive position – the unken reflex, which likely inspired some Pokémon characters - where they extend their limbs, raise their heads while closing their eyes, and turn up their tail over their body curling the tip. But what really threatens them is human-driven terrestrial and freshwater habitat loss and degradation, and the release of non-native salamanders in their territory.
#126 Sweet flag
The Sweet flag, Acorus calamus, might not look unique, but it's highly valued across several cultures mainly due to its notorious roots. Growing on the margins of shallow nutrient-rich water and streams, canals, fishponds, and lakes, this wetland species is renowned for its long history as a medicinal plant. Mentioned by the father of modern medicine – Hippocrates - it has been used since ancient times as a hallucinogen and an old folk remedy for treating arthritis, diarrhea, hair loss, and other disorders. And there’s more - this semi-aquatic species is multifaceted, used to flavour pipe tobacco; to purify sewage due to its high tolerance for ammonia and anoxia; in perfumes due to its sweet fragrance, among other. To this day, Sweet flag is studied for its various pharmacological properties, but there are still safety concerns around its toxicity – especially carcinogenicity. Since 1968, this species and its products have been banned as human food or food additive in the USA, and its use is regulated in Europe. Probably due to its versatility – and high pollution tolerance - it became widespread, even generating discussion of its real native range. Most likely native to subtropical Asia, it's non-native throughout much of Europe and southern North America. Although listed as Least Concern by IUCN, there are some local extinctions records. In addition to a growing demand for the drug markets, this species is under threat – like most medicinal plants - from habitat fragmentation, deforestation, and overharvesting. It's time we value our freshwater habitats for all the benefits they safeguard for humans and nature.
#125 Water stick insect
As it often happens with freshwater species, it’s possible to cross paths with the Water stick insect, Ranatra linearis, without ever knowing. With its weird stick-shaped body, this aquatic insect is commonly mistaken for other objects or its terrestrial look-alike. They also usually go unnoticed by their game – hiding in shallow and densely vegetated bodies of water, they cling parallel to the underside of leaves, waiting for unsuspecting prey to come within reach. Striking with their specialised raptorial front legs, they pierce the captured prey with a tube-like mouthpart and inject them with venom, causing tremors and eventually paralysis. This sit-and-wait ambush predator spends most of its time in water environments waiting for prey, including young ﬁsh, insect larvae, small crustaceans, and quite notably, the lesser water boatmen. Compared to other insects, they have long legs, which likely helps them capture the water boatmen, one of the fastest swimming aquatic insects. Belonging to the same family as water scorpions (Nepidae), they also have a long breathing syphon (tube) at the end of their abdomen to pierce the water surface for air, sometimes mistaken for a stinger. Commonly found in fresh or brackish waters of Eurasia and North Africa, this insect of around 35 mm - 50 mm is recorded as the largest animal found in hypersaline water bodies - water at a salinity greater than 24 grams p/L, saltier than ocean water. Although appearing wingless, adults have stiff wings that lean on their backs at rest. Most water bugs are impressive fliers, but not the Water stick insect, which is a bit clumsily. They fly mostly to move to another pond in case their own starts to dry up during the summer months.
#124 cuckoo catfish
The cuckoo catfish, Synodontis multipunctatus, is endemic to one of Africa's Great Lakes - Lake Tanganyika. This freshwater fish is named after the cuckoo bird due to their shared (in)famous reproductive strategy - brood parasitism - that includes finding unaware foster parents for their offspring. The cuckoo catfish is a member of a small group of squeaker catfishes (family Mochokidae), but it is the only one to smuggle its eggs into the care of another species - thick-lipped cichlids. These mouthbrooding cichlids lay their eggs in specially prepared nests, and females collect their eggs immediately after spawning to incubate them in their mouths for about three weeks. Cuckoo catfish exploit the cichlid's parental care by invading their nests at spawning time and creating enough chaos to quickly deposit their cuckoo eggs, which are mistakenly scooped up by the unsuspecting female "surrogate". Male cichlids do respond aggressively to the intruding cuckoo groups, but they get overwhelmed by repeated advances. Although the eggs are not similar - catfish's eggs are different in shape and smaller - cichlid females have to act quickly as their own eggs are at risk of being eaten by the invader. Recent studies show that females co-existing with cuckoo catfish may be able to selectively reject its eggs, but how it's still unknown. Having a cuckoo catfish as a stepsibling can be fatal for baby cichlids - catfish eggs hatch earlier, and they devour the cichlid's embryos over several days. This and other astonishing behaviour in our richly biodiverse freshwaters are still mostly unknown – and we might never get to know them if we don't protect these habitats.
#123 Dice snake
Also known as the Water snake, the Dice snake, Natrix tessellata, holds the title of one of Europe’s most aquatic snakes. Living near rivers, coasts, streams, lakes, ponds, and the surrounding terrestrial habitat, it is adapted to prey underwater. With a preference for fish and frogs, Dice snakes use frontal strikes to capture these prey underwater, assisted by their visual system that allows for better focus when submerged than other similar species. Females of this species are bigger than males, and both are active diurnally and nocturnally. During the hottest months, however, it’s almost entirely nocturnal in southern parts of its range, making it more difficult to spot its sometimes vividly coloured belly in yellow or orange with black spots - very similar to dice, ergo the name. Nonvenomous, this harmless snake has a wide Eurasian distribution, and it is also present in Egypt. Listed as Least Concern by the IUCN Red List of Threatened Species, their populations are decreasing, and there are reports of local extinctions due to habitat deterioration. They are threatened by the loss or modification of wetland habitats caused by, for example, river channelization and lake-shore development.
#122 wATTLED cRANE
Wattled cranes, Bugeranus carunculatus, are Africa's largest and rarest crane. They once ranged from coastal west of Africa to the African horn down to the southern tip of Africa, but nowadays are mostly concentrated in the Okavango delta. Listed as Vulnerable by the IUCN Red List of Threatened Species, their populations have suffered significant declines in southern Africa over the past few decades, especially due to wetlands degradation. This species is the most wetland-dependent of Africa's crane species - relatively intact wetlands like Cuando represent, therefore, an important refuge for these birds. They feed mainly on tubers and rhizomes of aquatic vegetation and large invertebrates and small vertebrates. Generally, they are also not migratory, but those that inhabit seasonal wetlands are irregularly nomadic in response to water availability. They are often seen in pairs – or trios with young birds – where the male tends to be larger than the female. They are usually silent and territorial when in pairs, but they can be seen in larger "floater" flocks.
#121 Smooth-coated Otter
The Smooth-coated otter, Lutrogale perspicillata, is the largest otter species in Asia. Found in South Asia and Southeast Asia’s slow-flowing waters typical of rice paddies and floodplains, and large rivers in some regions, they have a large distribution that is slowly and steadily decreasing. It was once widespread from the Middle East to southeast Asia, but its biggest asset became a problem – its short, smooth velvety fur is attractive to the illegal wildlife trade. The smooth two-layered fur - warm chocolate brown on the back and soft grey on the stomach - helps keep the underfur dry underwater to retain body heat. Mainly nocturnal, this species forms large, vocal family groups that prey together on fish, shrimps, frogs, crabs, insects, and birds. They catch prey with their sharp claws on their webbed paws, which boost their swimming abilities together with their paddle-like flat tail. Listed as Vulnerable by the IUCN, habitat degradation and loss due to increasing anthropogenic pressure on wetlands and waterways threaten these otters. They need thick riverside vegetation to hide, dig dens and raise cubs. In addition, illegal trapping for the fur trade has recently taken a heavy toll in many of their range countries, and law enforcement is lacking. They are also wanted as pets and for traditional medicine.
#120 Brown trout
The brown trout, Salmo trutta, is a migratory fish native to the cold rivers and lakes of Europe, spawning in rivers and streams with clean gravel beds. Due to its high value to fisheries, it has been introduced to many rivers globally, sadly becoming an invasive species in some areas like North America. Adults are easily mistaken for the Atlantic salmon, as they have spots under the lateral line while the Atlantic salmon do not. The migrating populations are also called sea trout - they generally feed in freshwater and usually go to the sea after spawning. Females are the ones that select the spawning sites, where they form spawning beds called redd –bowl-shaped indentations of clean, bright rocks - by beating the rocks with their tail-fin to remove moss, dirt, bigger rocks, and debris. The male's role is to guard and defend the females against other males, and after fertilizing the eggs, females over the eggs with gravel. This species is threatened locally by pollution (especially the eggs), impacts from salmon farming (e.g., sea lice), and dams. For example, the Vistula River in Poland had a large sea trout population, which was able to migrate until the Carpathian mountain tributaries, almost 1,000 km from the sea. However, after the dam of Włocławek was constructed in the 60s, sea trout have been observed above the dam only occasionally, disappearing from the upper part of the basin.
#119 Indus valley bullfrog
Indus Valley bullfrog, Holobatrachus tigerinus, a.k.a Indian bullfrog, is one of the largest frogs on the Pakistani plains. Found in the freshwater wetlands - natural and artificial – of Pakistan’s Indus River basin, this frog can hibernate during winter and drought by burrowing itself in soil. It is also common in paddy fields and moist riparian areas of Afghanistan, Bangladesh, Bhutan, India, Myanmar, and Nepal. Sadly, it has been introduced to Madagascar and Maldives, which can have a negative impact on the invaded ecosystem’s integrity. Indus Valley bullfrogs are voracious feeders - anything that is moving is game, bounced upon, and swallowed. If needed, they use their anterior limbs to thrust larger food into their mouth, including mice, young frogs, juvenile snakes, and small birds. They don’t tend to stay in water for long – when danger approaches, they plunge into deep water using their almost fully webbed feet and stay underwater for a few minutes. If in clear pools,they hide under bottom gravel. With the beginning of the monsoon, a large number may be seen all over the fields around temporary water pools. And many of them will be easier to spot due to their recently acquired lemon-yellow colour. Yes, this species can change colours – during the breeding season, males turn yellow and their deep blue vocal sacs more prominent, while females remain dull and drab-coloured. Sitting close to each other in shallow water, calling males repeat their powerful nasal call several times, now and then jumping over each other. Lurching around, females are grabbed by the males when in range, and after some fighting with the neighbours, the pair somehow moves to a quieter place to lay the eggs. This species is listed as Least Concern by IUCN Red List.
#118 Ocellate river stingray
The Ocellate river stingray, Potamotrygon motoro, is the most abundant and widespread river stingray species across South America, occurring in the rivers of the magnificent basins of Uruguay, Paraná-Paraguay, Orinoco, and Amazon. Like many river rays, it prefers calm waters, especially sandy margins. Although most commonly seen when water levels are low, this species is found in both shallow- and deep- waters, as well as clear and murky. Generally, they are found still and hiding, partly burying themselves, especially during the warmest period of the day. When seen in shallow water, artisanal and commercial fishers catch them mainly for their meat. But due to their attractive patterns of dark-ringed orange spots, they are also collected for the ornamental fish trade, especially juveniles. But mishandling this species might come with a painful, but not deadly, price – their tail has a venomous sting, which they use to protect themselves when feeling threatened or when unaware bystanders step on them. According to scientists, this curious species can also discriminate colours and process numerical information. And females usually give birth to an odd-sized offspring, varying from 3-21. Even though they are listed as Data Deficient, their freshwaters, especially the River Paraná, are at risk of habitat degradation caused by damming, navigation, hydroelectric plants, and the construction of many ports along the river.
#116 Dalma Snail
The Dalma snail, Hauffenia kissdalmae, is a member of the most species-rich freshwater snail family, Hydrobiidae (spring snails). This family encompasses tiny creatures, mostly living in very clean and well-oxygenated waters, springs, small streams, cave streams. Many are narrow-range endemic species, occurring within the drainage of one single streamlet or even in one single spring or cave. That might be the case of the Dalma snail, discovered in a small spring in the Börzsöny Mts, in Hungary in 2008. This species inhabits the' shallow subterranean habitat' - fissures and cavities in the bedrock close to the surface. In 2011, it was listed as Data Deficient by IUCN because its exact distribution and population numbers were unknown. Since then, intensive research revealed about 40-50 populations in the Slovak and Hungarian part of the Northern Carpathians, distributed over an area of around 800 km2. Although one might think that its underground lifestyle would guarantee them safety, a recent study suggests otherwise. Feeding on bacteria living in the delicate net of tree rootlets, their survival depends heavily on the constant forest cover and the presence of old trees. The fate of a Slovak population monitored between 2012 and 2021 illustrates their vulnerability - in 2014, deforestation occurred in this population's spring vicinity. After that, fewer and fewer live specimens were found until they disappeared entirely after a few years. This case highlights the complex relationships and interactions between organisms within an ecosystem and how little we know about them. And in particular, how easy it is to destroy these fragile systems.
The waterbuck, Kobus ellipsiprymnus, is a highly water-dependent mammal. It is usually only found “at or near water” due to its high susceptibility to dehydration and overheating relative to other African bovids. This medium-sized (150–300 kg) antelope occurs widely throughout Africa, in habitats like lakeshores, riverine woodlands, and open grasslands, including the dazzling Hluhluwe-Imfolozi Park in South Africa, where the life-giving Imfolozi River boasts rich biodiversity. Waterbucks have a reputation of being smelly due to a musky oil secreted by glands in their skin, which forms a waterproof layer around the hair, protecting their skin when they enter the water. They have been known to dash into water to evade predators like lions and leopards. They also exhibit strong territorial behavior, where males defend areas close to water with abundant and high-quality forage. Although listed as Least Concern by the IUCN Red List, this species’ populations are declining due to hunting.
#114 Hooded Grebe
The Hooded Grebe, Podiceps gallardoi, moves like no other bird. With the South American lakes as their stage, they perform an unusual courtship dance sometimes referred to as "Tango in the Wind". The dancing ritual combines rigorous headbanging displays, occasional diving, and some intense stare-downs, and the suitor with more rhythm, stamina, and coordination tends to be the fitter partner. Striking also in appearance, this exquisite bird is unique on many fronts – it's a rare endemic species, with the only known wintering grounds located at the estuaries of Río Coyle, Río Gallegos, and Río Chico on the Atlantic coast of Santa Cruz, in Argentina. The breeding season arrives with springtime, when they migrate to the Patagonian steppe to set up nesting colonies on a few interior lakes. Very few people reach this region, so these aquatic birds were found only a little over 40 years ago. But, sadly, they are already Critically Endangered. Nowadays, just 750 breeding adults are left – an 80% plummet since the 1980s. The lakes suitable for their breeding are reducing at an uncommonly fast pace due to climate change, which also aids and bolsters the impact of three invasive species – a fish, a bird, and a mammal. The Rainbow trout, Oncorhynchus mykiss, changes the entire food chain, devouring the same freshwater invertebrates that these grebes usually feed on and likely preventing the growth of the only aquatic plant in these lakes, essential to building the grebes’ floating nests. The Kelp Gull, Larus dominicanus, recently arrived at the highland plateaus, preying on colonies during a critical moment of their life cycle - the egg-laying phase. The most devastating effect comes from the predation by the American Mink, Neovison vison. But it's still possible to prevent the extinction of this unique dancer. Urgent conservation action is underway via initiatives such as the Hooded Grebe Project.
#115 Ganges river dolphin
The Ganges river dolphin, Platanista gangetica gangetica, is one of the most ancient dolphin species still alive, being considered a living fossil. It is known as the "Tiger of the Ganges" due to its role as a top predator and an ecosystem indicator species – like a tiger is in its habitat. This species has many common names, which in local languages are reminiscent of the dolphin's breathing noise like "susu". But they are generally shy towards humans and most often found alone. With extremely poor eyesight, they rely almost entirely on echolocation to navigate and locate their prey, usually fish and crustaceans. They are found only in the river systems of the Ganges-Brahmaputra-Meghna, and nearby Karnaphuli-Sangu River, in Bangladesh, India, and Nepal. Like the Indus river dolphins, they have a particular side swimming behaviour that helps them navigate shallow waters. In the past, during the monsoon season, these dolphins would move upstream into smaller rivers and then back downstream to larger channels in the low water winter. But nowadays, dams and barrages restrict their movement. They are under great threat due to proposed and ongoing large infrastructure projects, which can also destroy their habitat and decline river flows. Listed as Endangered by the IUCN Red List of Threatened Species, they are also at risk because of fisheries bycatch and pollution. But there's hope for the Ganges river dolphin. They are legally protected in all the countries in which it lives. And WWF's initiatives like River Dolphin Rivers tackles the systemic threats – unsustainable fisheries, hydropower and infrastructure, and pollution –, also protecting their habitats for the benefit of people and nature (Learn more about this species with this video).
#113 New Guinea Crocodile
The New Guinea crocodile, Crocodylus novaeguineae, is a medium-sized crocodile that prefers swimming in New Guinea island's vast freshwater systems like rivers, swamps, and marshes. Restricted to the island of Papua New Guinea and Papua including Pulau Kimaam , this species can grow up to 3 m for females and 3.5 m for males, especially in the Sepik River, where larger animals can be found. The Sepik is one of the largest rivers in the Asia-Pacific region, harbouring some of the world's largest freshwater and saltwater crocodile populations. Sepik's crocodile species, including the New Guinea crocodile, have cultural significance to the communities living across the river - they pay them tribute every year with a three-day Crocodile Festival. Inspiring cultural traditions, beliefs, and legends, this ancient animal symbolises strength, power, and manhood. Man and crocodile share a special bond in Sepik culture, literally embodied by men proudly wearing scars that resemble the back of a crocodile. It's during the rite of passage of skin-cutting initiations that they cut these scars into their skin from shoulder to hip. Listed as Least Concern by the IUCN, this species' populations benefit from the vast areas of wetland habitats and low human population density in Papua New Guinea and Papua. Management programs regulate exploitation while providing equitable economic incentives to indigenous landowners. There are threats from introduced fish (Pacu, Piaractus brachtpomus) and mining which could increase in future. Plans to develop the largest mines in the country on one of Sepik's major tributaries threaten the future of the river basin, its people, and nature. But the people of the Sepik are fighting to save their river and all it offers them.
#112 Fire-bellied toad
The Fire-bellied toad, Bombina bombina, it's known for its namesake black and red-orangish markings on the belly and its melancholic call. Found in Central and Eastern Europe, this toad prefers living in stillwaters including lakes, ponds, swamps, peat bogs, ditches, flooded rice fields, and quarries. When faced with potential predators, Fire-bellied toads have curious reactions like the defensive posture called the "unkenreflex" – they turn over and curve their bright belly upward, covering the eyes with their palms. Or, instead of turning over, it bends its body downward, lifts up the head, and curves the extremities showing the bright spots on its flanks and the extremities' ventral surface. This behaviour adds to its survival strategy - even though it has venomous skin secretions, many vertebrates regularly consume these toads. Staying mainly in the water or near the shore, during winter they hibernate in the mud on the bottom of water bodies or land. When the breeding season starts, males vocalize floating on the water surface, with their bodies flattened, and sometimes they can call from under the water. For breeding, they prefer shallow ponds as these warm up quickly and have plenty of submerged aquatic vegetation. They stay in ponds after breeding, but these ponds can dry up in late summer. This species is rapidly declining in Germany because these ponds are currently disappearing - in Lower Saxony, it is now only present in the Elbe Floodplain. Although listed as Least Concern by IUCN, the Fire-bellied toad is significantly declining or extinct in many areas, especially West Europe. The most serious threat is wetlands' destruction.
#110 Amazon Molly
Contrary to what its name might suggest, the Amazon molly, Poecilia Formosa, does not live in the Amazon River basin. Rather, it swims the waters of the Rio Grande/Bravo lower basin and Tuxpan and Nueces rivers. The reason for its name is because it consists almost entirely of females – like the Amazons, a tribe of warrior women from Greek mythology. This inconspicuous fish is one of the few asexual vertebrates in the world, having originated by hybridization. They reproduce via gynogenesis – they simply clone themselves, not producing any male offspring. But unlike other asexual organisms, Amazon mollies still need help to reproduce – they mate with closely related Molly fish, from which they obtain sperm that will trigger the cloning process. However, none of the male’s genes is incorporated into the offspring’s DNA – instead, it is completely destroyed. Researchers from the Universität Würzburg studied how the Amazon molly still exists, as according to established theories, it should have been extinct during the course of evolution. Their central insight was that this species has a unique genetic variability, especially high for relevant genes of the immune system, and clear signs of an ongoing evolutionary process. This rare vertebrate is listed as Least Concern by IUCN, being represented by many subpopulations and locations. But the population trend is unknown and its clear and muddy freshwater habitats, like the Rio Grande/Bravo River, are under pressure from climate change, dams infrastructure, irrigation, among other threats.
#111 Zambezi shark
The Zambezi shark, Carcharhinus leucas, a.k.a. bull shark, is one of the few shark species known to travel long distances into rivers systems and remain there for long periods. Famous for this ability, it's also named after the mighty Zambezi, where it reached up to 1120km away from the ocean. But they also swim other rivers – and even hypersaline lakes - worldwide, with a record of 5080km away from the ocean in the Amazon/Ucayali River. But why and how do they do that? They rely on estuaries and rivers as nursery habitats, where pregnant females give birth and juveniles can remain for five years. They are a fully euryhaline species, able to move easily between marine and freshwater habitats thanks to osmoregulation - their body acclimates to changes in salinity via independent regulation of sodium/chloride and urea levels. This adaptation favours their broad range, including coastlines of all three big oceans (Atlantic, Indian, Pacific) in both hemispheres, with evidence of their presence in 415 fresh and brackish water localities. Reaching up to 4m in length, they are named Bull sharks due to their short, blunt snout and tendency to head-butt their prey before attacking. They are generalist predators and eat almost anything they see - fish, including other sharks, and also dolphins, birds, turtles and invertebrates. This species is listed as Vulnerable by the IUCN due to fishing as a target for meat and fins and a bycatch. In addition, their habitat preference means they are also threatened, especially juveniles, by habitat loss and degradation, including damming, pollution, and climate change. In the Zambezi River, the Cabora Bassa Dam wall and the Kariba Dam currently prevent this species' migration to the river's upper reaches.
#109 Yangtze Giant softshell turtle
The Yangtze Giant softshell turtle, Rafetus swinhoei, is one of the world’s rarest reptiles. Reaching around 120 kg in size, this enormous freshwater turtle is a bit strange-looking with its long flat carapace, soft body, pig nose, and a long neck capable of “periscoping” like an otter. Due to its rarity, we know very little about them - adults seem to be omnivorous, fairly sedentary and reach up to 100 years. They are worshipped in some areas - Vietnamese mythology says this enormous turtle is the living representative of the Great Turtle God, Kim Qui. But not even its god-like status could save them - they are one of the most severely threatened species on Earth. Listed as Critically Endangered, only four surviving individuals are known - two of which are in captivity, and none have reproduced successfully recently. Decades of dam-building likely fragmented populations, getting several turtles stranded in lakes and reservoirs. This species is also at the brink of extinction due to exploitation of adults and eggs for (subsistence) consumption and targeted capture attempts in recent years, habitat loss for agriculture like rice paddies, pollution of wetlands and riparian habitats, and sand mining. Historically, this species inhabited the Red River of Yunnan and Viet Nam and the lower Yangtze River floodplain. Nowadays, its area of occupancy is less than 10km2 after a population reduction of over 99% over the last two generations. But we can’t give up on these divine turtles. Captive breeding efforts continue, and field surveys to locate additional animals in the wild. The Asian Turtle Program works with villagers and stakeholders to protect and monitor the two known wild individuals in Viet Nam. And WWF’s Emergency Recovery Plan outlines how to reverse the rapid decline of their critical freshwater habitats.
#108 Rio Grande silvery minnow
The Rio Grande silvery minnow, Hybognathus amarus, is one of the most Endangered fish species of North America. It was once widespread and abundant, swimming the river basins of Rio Pecos and Rio Grande/Bravo in Texas, New Mexico, and Mexico. Nowadays, it is only seen in a 280km stretch in New Mexico - from Cochiti Dam to the headwaters of Elephant Butte Reservoir. Even though they prefer the basin’s low-flow and perennial streams and rivers, they reproduce when there is higher flow. Pursuing a single female, the male nudges the female’s abdominal region and wraps himself around her when she is ready to spawn. They spawn together, with males presenting several spawning episodes with 10 minutes intervals. Thousands of semi-buoyant, non-adhesive eggs, will then passively drift downstream while developing. But all this strategy might not pay-off if the river they rely on continues to run dry due to frequent droughts such as have occured in recent decades. Their populations have already declined greatly due to the historical demand on the waters of the Rio Grande/Bravo for agricultural activities, which led to habitat destruction and modification for water allocation and dams, fragmenting their populations. This species also faces competition and predation by non-native species, and is also at risk from pollution. Although some of these have been reduced since the Rio Grande Silvery Minnow was listed as Endangered, none have been eliminated. Coupled to climate change, this species that depends on side channels and overbanking flows during flooding is being pushed to the brink of extinction.
#107 Siamese tiger perch
The dazzling stripes of the Siamese tiger perch, Datnioides pulcher, used to brighten up the rivers of the Indo-China area, from the Mae Klong and Chao Phraya basins to the middle and lower reaches of the mighty Mekong. Extirpated from Thailand in the 1990s, this Critically Endangered fish is now rare in Cambodia, Vietnam, and Lao PDR. The attractive vertical yellow and black patterns are the main reason for its demise - researchers estimate that its global population has declined by more than 90% over the past 20 years after high levels of exploitation for the international aquarium trade. Although rarely seen, it is still fished for this purpose when found. In addition to overfishing, the Siamese tiger perch faces major threats from habitat destruction and degradation from dams and infrastructure in tributaries (small dams, weirs, locks), blocking paths between the main river and tributaries. And this tiger perch does like to swim these waterways, including larger lakes connected to rivers, preferring habitats with submerged woods and rocky crevices. Growing up to 40cm, this tiger perch feeds on fishes and shrimps and was once a popular food fish in Thailand and Cambodia. Artificial breeding has been attempted since the 1990s in Thailand to try bending the curve of its populations, but without success. The species is also protected – it is illegal to catch or possess it. But this law is written under its previous scientific name (Coius pulcher), creating issues when implementing it. And there are many other species on the brink of extinction, and many we don't even know exist. The Mekong River Basin is home to astonishing biodiversity, and hundreds of new species are still discovered every year – WWF's report shows over 200 species identified in the Greater Mekong area just in 2020. The Siamese tiger perch is just one of 95 fishes. The Asian Species Action Partnership (ASAP!) , which is a platform with over 200 organizations including WWF, aims to end species extinction in Southeast Asia.
#106 Ruddy shelduck
The striking Ruddy shelduck, Tadorna Ferruginea, is a gooselike duck - when in flight, they can look as heavy as a goose. But they are also good swimmers, living around freshwater bodies like wetlands, rivers, and marshes from the Mediterranean basin to Asia. They are mainly nocturnal and omnivorous - their diet includes seeds, grasses, aquatic plants and invertebrates. This species is more than just a pretty orange-brown plumage – it's also quite tough, resisting extremely cold temperatures and rigid climates. Nowadays, they are becoming rarer in southeast Europe, but Ruddy Shelducks are still common across much of its Asian range. Breeding in southeast Europe and Central Asia, most populations migrate to South Asia during winter. Resident and sedentary populations are rare, but some small ones are in northwest Africa, like in the Sebou River basin and Ethiopia. Their movements are linked to the availability of suitable water (moving away from drought-affected areas or to temporary wetlands). Usually, they are in pairs or small groups along rivers. When it's time to breed, a couple forms a close bond, and you can spot the male due to a temporary black ring at the bottom of its neck. After breeding, they cannot fly for a month – adults undergo shedding and regrowing feathers called moulting. During winter and moulting, we might see them congregating into larger flocks, making it even easier to hear them from big distances – they have a particularly loud honking-like call. Although listed as Least Concern, their breeding grounds and stop-over wetlands are being rapidly drained and filled for urban, industrial, and agricultural uses. WWF's Asian Flyways initiative works to protect these pathways and the many marvellous migratory birds that visit them.
#105 Yacare caiman
The Caiman yacare is an iconic freshwater reptile of South America. They swim the freshwater rivers and wetlands of Paraguay, Northern Argentina, Southern Brazil and Bolivia, being especially well-known in the world’s largest tropical wetland - the Pantanal. They are even named after their mesmerizing habitat in Brazil, being called “Jacaré-do-pantanal” (Pantanal’s yacare). And they also go by a curious nickname, “Jacaré-piranha” (Yacare-piranha), since even with their mouth closed, they show many teeth. They feed mainly on fish and aquatic invertebrates, but their diet also includes birds, reptiles, and mammals. When fishing, this species uses a tactic similar to other caimans called collective fishing, where 2 to 15 animals line up in a channel against the current and grab passing fish without individual aggression. It is a medium-sized crocodilian, with male Yacares reaching up to 3m in length and females 2,5m. The mound-nester females place the nests close to canals and rivers, guarding them – behaviour apparently influenced by human hunting pressure – and defending their offspring aggressively when juveniles hatch. Even though abundant, widely distributed, and listed as Least Concern, this species is subject to ranching wild harvest, and its habitat faces many threats. The river that feeds the Pantanal, the Paraguay River, is threatened by hydropower plants. The region also faces agriculture expansion, engineering work for navigation, and climate change.
#104 Dwarf sturgeon
The endemic Dwarf sturgeon, Pseudoscaphirhynchus hermanni, is also known as the small Amu Darya shovelnose sturgeon. As its namesake hints, this is a small, rare sturgeon only present in the muddy waters of the Amu Darya River in Central Asia. The enigmatic Dwarf sturgeon is identifiable by its lack of a caudal filament and spines on the snout, a shovel-shaped snout, pectoral fins with a fold that curls dorsally, and of course, its small size. It is poorly studied due to its rarity – its spawning grounds are uncertain, and its generation length is estimated to be from 3 to 8 years due to its smaller size than similar species. The available data shows that Dwarf sturgeon populations are declining, as their range has declined drastically in the past 30 years. The Aral Sea's ecological disaster - which included its drying due to massive water allocation for irrigation, pesticide pollution, and habitat degradation - extirpated this species from the area and the lower Amu Darya. Since then, the Amu Darya River basin has faced habitat alterations from water abstraction, pollution, damming, and channel management, threatening the river's health and biodiversity. Also threatened by poaching, the IUCN Red List of Threatened Species lists the Dwarf sturgeon as Critically Endangered. It was last caught in 1996 in the middle reaches of the Amu Darya, and the last records from the lower reaches are from 1982. However, there is still hope for this rare sturgeon – there are currently unconfirmed fishers’ (poachers) reports catching them, and a study from 2020 confirms they are still there. Part of the species' range is within a nature reserve (Amu Darya Nature Reserve), and WWF's conservation efforts include the Sturgeon initiative and WWF-Russia's on-the-ground work on sustainable fisheries.
#103 Red lechwe
The Red lechwe, Kobus leche leche, is a mammal associated with wetlands, preferring the shallow water margins of floodplains and swamps and occasionally swimming across deep-water areas. It is the most widespread subspecies of the Southern Lechwe (Kobus leche) - commonly seen grazing the wetlands of south-central Africa, including in the magnificent Okavango Delta in Botswana and the Linyanti swamps of the Caprivi Strip, Namibia. Southern Lechwes are medium-sized antelopes that have adapted to their wet environment by having distinctly elongated hooves. Red lechwes feed on the lush green aquatic and semi-aquatic grasses, being particularly dependent on this environment and, therefore, an important indicator species. Lechwes' males (a.k.a. rams) are the only ones to carry lyrate-shaped horns. They are territorial, and males that fail to establish territories congregate in bachelor herds. Females (a.k.a ewes) form breeding herds with their offspring, moving freely between ram territories – males compete for mating favours only when receptive ewes are within their domains. Breeding is not strictly seasonal, especially not amongst Red Lechwe's Botswana populations. When about to give birth to single lambs, pregnant females leave the herd to find cover on clumps of bushes, where they keep their offspring hidden for two to three weeks. Sadly, due to poaching, expansion of agriculture and livestock grazing, changes in water management regimes, drought, and encroachment by alien plant species, The IUCN lists the Southern Lechwe as Near-Threatened, and there is also evidence of Red Lechwe populations' decline over the past years.
#102 European grayling
The European grayling, Thymallus thymallus, is part of the salmon family. But unlike many salmonids, this species is generally potadromous, meaning they migrate only within freshwater. European graylings swim in Europe’s submontane rivers with a hard sand or stone bottom and well oxygenated, cold, and fast-flowing water. They are an indicator species for the ecological integrity of the whole river region. They spawn in shallow stretches or riffles, where males defend their small territories until spawning starts. The IUCN Lists this species as Least Concern, but the last assessment was in 2011, while recent studies show that grayling stocks have declined in the previous decades. They are becoming increasingly vulnerable to climate change and under regional threats such as pollution, and dams and river regulation infrastructure. In the European Alps, 80% of all larger rivers are affected by diverse hydromorphological impacts. And there are plans for more infrastructure in the region, like in the Isel river. Instream connectivity plays a fundamental role for many fish species, including this medium-distance migratory species that requires an open river corridor for spawning migrations and movements between habitats. Even though some infrastructure has a fish passage, not all fish can use them. Most importantly, dams and reservoirs alter the natural flow of water and sediment, affecting this species that is an indicator of river health and an entire ecosystem downstream.
Tucuxi, Sotalia fluviatilis, is the guardian of the river and a symbol of good luck, according to the local communities of the Amazon River basin, including the Tapajós river. This positive image is thanks to its ability to avoid rocky and shallow waters, guiding boats to safe river sections. The Tucuxi swims in Brazil, Colombia, Ecuador, and Peru. This species overlaps in range with the Amazon river dolphin, but it is easy to distinguish them, as it is smaller, tends to be in larger groups, and swims faster. This is the only river dolphin that jumps like marine dolphins, and it is perceived as vivacious and sociable. They rely heavily on echolocation to communicate, navigate, and find food in the dark and sometimes turbid waters like other dolphin species. Scientists believe that they prey on various fish species and crustaceans, but studies are scarce. Sadly, they are listed as Endangered due to death caused by fishing gear, habitat degradation due to dams, pollution from gold mining, navigation, and sand and gravel mining. WWF’s River Dolphin Rivers initiative focuses on eliminating the use of gillnets – curtains of fishing nets that hang in the water – and preventing new dams to stop their population decline and enable them to recover. The Tucuxi is also included in international legislation such as the Convention on Migratory Species (CMS). Recently, conservation action plans were put in place for the species at both national and continent-wide levels. Learn more about this river dolphin here.
#100 New Hairy crayfish
The New Hairy crayfish, Euastacus neohirsutus, is endemic to the small and cool creeks fringed by Australia’s rainforest in New South Wales. They are considered widespread within their relatively small range, which includes the Orara and Nymboida Rivers systems. The New Hairy crayfish is part of the Euastacus genus, recognizable by short, robust spikes on its claws, carapace, and abdomen. They are opportunistic omnivores, eating both plant and animal matter, and are rather aggressive and territorial. Their lifespan starts with a relatively long attachment to their mother - after breeding in response to environmental triggers, like a drop in water temperature and stream levels, the eggs remain attached to the mother for 5-6 months until they hatch. It’s only when the newly hatched young shed their outer layer that they lose the connection with their mother. They are slow “growers”, with females taking 7-9 years to reach sexual maturity. The New Hairy crayfish breeds once a year around June, releasing the juveniles around December. IUCN estimated that 82% of Euastacus species were threatened in 2010. The New Hairy crayfish is listed as Least Concern, but it presents fragmented populations. Euastacus crayfish rely on streams for survival, but these are under pressure from habitat destruction, pollution and reduced water quality, the introduction of exotic species, and illegal collection by humans.
#99 Malatgan River Caecilian
The Malatgan River Caecilian, Ichthyophis weberi, was a “lost” species up to 2015. It was not seen for about 60 years until researchers found one near the Malatgan River in Palawan, Philippines. Caecilians are part of a group of legless amphibians, most species spending the best part of their lives below ground or plying the waters of shallow streams. Malatgan River Caecilians are no different – they live in riverine habitats, usually river banks in lowland forest and adults are likely to be subterranean. Unsurprisingly, much remains unknown about this species, including its breeding strategy and the low number of recordings, which may be explained by its natural rarity or secretive ground-digging behavior. The IUCN Red List of Threatened Species lists them as Endangered due to habitat destruction, especially lowland forests, which results in the degradation of streams and creeks. But there are reasons to be optimistic thanks to the efforts of Fins and Leaves, the NGO that led the expedition for the rediscovery of Malatgan River Caecilians. They also led the work to declare the Cleopatra’s Needle Mountain Range, where this species is found, as a protected area.
#98 Saddle-bill stork
The striking Saddle-bill stork, Ephippiorhynchus senegalensis, is a widely distributed wading bird in the African continent. This remarkable species lives at large undisturbed wetlands and rivers, generally found near water bodies so it can forage for its favorite fish prey (and eventually crabs, frogs, birds, and insects) with its unique red, yellow and black bill. Growing up to 150 cm in height, it is one of the tallest storks in the world. Saddle-bill storks are mostly resident, with no evidence of regular long-distance migration. Females and males generally nest in solitary pairs and remain that way when not breeding. The easiest way to tell them apart is through their eyes - females have yellow eyes while males are dark-brown. Even though they are listed as Least Concern by the IUCN Red List of Threatened Species, their populations are decreasing due to wetland degradation (e.g., pesticide contamination) and conversion to agriculture.
#97 Chindongo demasoni
The colourful Chindongo demasoni is a small fish endemic to Lake Malawi in Tanzania. This eight centimetres cichlid occurs at the lake’s small reefs, with a population also thought to be small. IUCN assesses their population as Vulnerable due to threats from sedimentation and over-collection for the ornamental trade. The striking fish inhabits intermediate, stony and rocky substrates in shallow waters, feeding on a mixture of algae, cyanobacteria, heterotrophic microbes, and detritus. Unlike many Malawian fish species males and females have the same colour: a bright light blue body with dark blue/purple to almost black vertical stripes. They differ slightly in terms of length, where the male is a bit bigger than the female. Like most Malawian cichlids, they are mouthbrooders – females will keep the fertilized eggs inside their mouth for about 21 days until their fry is ready for the world.
#95 TADPOLE SHRIMP
The tadpole shrimp, Triops longicaudatus, is a widely distributed living fossil. Although not really a shrimp, this species is part of a diverse and small group of ecologically important, largely freshwater primitive crustaceans. The broad shield-like double carapace covers most of their body, and when they swim, they present a unique outlook due to the arrangement and the movement of little “limbs” called phyllopods. These phyllopods beat sequentially and fast, forming spectacular wave-fronts. They also use phyllopods to feed, which moves the prey towards their mouth. They live on the bottom of temporary pools, ponds, and shallow lakes, feeding on all available food sources - living or dead organisms – to reach maturity and lay their eggs as soon as possible. Their eggs might be one of the reasons why the tadpole shrimp has been around for so long – they are almost impossible to kill and are even able to survive for decades. If environmental conditions are not favourable (e.g., extreme temperatures), the female will modify the fertilized eggs or “cysts/resting eggs'' to enter a state of dormancy, and they will only hatch once conditions improve. Due to the reduction in the number and quality of temporary wetlands, several species of tadpoles have been assessed as endangered by IUCN Red List of Species.
#94 indus river dolphin
On world river dolphins’ day, meet the Indus river dolphin, Platanista gangetica minor. Endemic to the naturally murky and silt-laden Indus river basin, this species is considered a living fossil together with the Ganges river dolphin, as they are the most ancient dolphin species still alive. Indus river dolphins are functionally blind, relying on echolocation clicks to navigate and find food like other dolphin species. But they emit sound almost constantly, which reflects the complexity of the river environment. As an adaptation to navigate through shallow waters, they developed a unique side swimming behaviour. They are not easy to spot – not only they are generally shy towards humans, but they also surface for only about 1 second before diving back for just over a minute. And, unlike other river dolphins, their dorsal fin is rather small and more like a triangular hump. In addition, this species is mainly solitary, even though it has occasionally been seen in groups consisting of as many as 30 individuals. Listed as Endangered by IUCN Red List of Threatened Species, the last 2000 individuals are mostly found in the lower parts of the Indus River in Pakistan. Their range has been reduced by around 80% due to the construction of irrigation barrages. They are also threatened by dams, entanglement in fishing nets, and pollution. These top-predators are indicators of the health of rivers which are the support system of economies and hundreds of millions of people. And that’s what initiatives like River Dolphin Rivers are trying to protect (check here one of the ways you can support the initiative).
#96 Water hyacinth
The Water Hyacinth, Eichhornia crassipes, is a South American species with beautiful purple and violet flowers. It grows in shallow temporary ponds, wetlands, marshes, and flowing waters, lakes, and rivers. In its native range, this free-flowing aquatic macrophyte has an important ecological role by providing food and refuge for many species, including waterfowl and waterbirds. It also determines the community composition of other plants, small aquatic microorganisms (including insect larvae and crustaceans), fish and other animals in its freshwater ecosystem. Even though it presents frost sensitivity, it generally tolerates extreme environments (e.g., nutrient supply, temperature), even growing in toxic water. Due to their striking flowers, they have been introduced in many parts of the world as ornamental plants. First records of the species date back to 1816 in Brazil, and its introduction to North America in the late 1800s. Sadly, they are currently known to cause significant ecological and socio‐economic effects and are described as invasive species when established outside their native range. They reproduce quickly, commonly forming dense, interlocking mats and their growth rate is facilitated by water bodies enriched by nutrients from agriculture and waste water – i.e., unhealthy freshwater ecosystems. Once established, the Water hyacinth is not easily removed as standard management and control strategies are costly and not entirely successful. WWF works with partners and local communities to find innovative solutions that are ecologically and socio-economically viable, besides creating awareness on the high risks of humans introducing species to habitats outside their native range. The Emergency Recovery Plan for Freshwater Biodiversity states that a key action is to prevent and control non-native species invasions. Although water hyacinth is problematic when introduced outside its native range, I think we can all appreciate its beauty and importance to its native ecosystem.
#93 Aquatic anole
This lizard is one of the most notable species in the animal kingdom, as it has mastered the art of “scuba-diving”. The Aquatic anole, Anolis aquaticus, is part of a remarkable group of lizards – the Anoles (genus Anolis), which have diversified in many ways to take advantage of their environment. Found along stream margins in the lowlands and premontane slopes of Costa Rica and Panama, Anolis aquaticus is a mid-sized semi-aquatic lizard recently made famous for spending up to 16 minutes underwater! Researcher Dr. Lindsey Swierk hypothesized that they adapted to evade predators by using a bubble attached to their snouts to recycle oxygen – like a scuba tank. Many other lizard species are known to escape from threats via water: some swim, either remaining at the surface or diving, while others use foot-slapping to run over water, and some even combine the two. Aquatic anoles use a combination of surface swimming and diving, jumping into (generally) small and slow-moving streams from the banks and boulders of their riparian habitats to which they are restricted. They swim for a short distance (up to a few meters) or are carried downstream by the current while “rebreathing” exhaled air that gets trapped between their skin and the surrounding water.
#92 Brown China-mark
Most of the lepidopterans (butterflies and moths) with a life cycle associated with aquatic habitats belong to the family of crambid snout moths. The Brown China-mark moth, Elophila nymphaeata, is part of this family - its larvae (a.k.a. caterpillars) are entirely aquatic and have developed various strategies and adaptations to stay underwater. Found in Europe and across the Palearctic to the Russian Far East and China, the adults live for just a few days and can be seen flying from June to September. Generally, they begin flying in the evening, lurking amongst the waterside vegetation during the day. Females crawl underwater and cling to water plants to lay their eggs on the lower side of floating leaves. When they hatch their eggs, the caterpillars start feeding on the leaves. Curiously, this species’ caterpillar constructs a flattened case around itself by spinning two oval pieces of leaves together. This case camouflages and protects the caterpillars, in addition to working as an oxygen reservoir as it’s filled with air and completely surrounds their bodies. They can either carry the case free with themselves or adhere it to their food-plant temporarily. Before becoming full adult beautiful moths, they have to through pupation, where they will spin cocoons of leaf pieces attached to the plant close to the water surface. The pupa connects to the air-ﬁlled intercellular cavities of the plant, from where it takes up oxygen. After quietly transforming themselves in 2-3 weeks, the adults fly into the last days of their lives to complete their life cycle.
#90 Siamese crocodile
The Siamese crocodile, Crocodylus siamensis, is an extremely rare freshwater species. It was once reasonably abundant in Southeast Asia, inhabiting freshwater swamps and slow-moving rivers of Thailand, parts of Vietnam, Cambodia, Lao PDR, and parts of the Malayan Peninsula and Indonesia. Sadly, this species disappeared from much of its range by the early 1990s, mainly due to hunting and harvesting. Its only significant remaining wild populations in Cambodia (200-400 individuals) and Indonesia (in Kalimantan) continue to face threats like habitat loss and degradation, hydropower dams, destructive illegal fishing methods, and poaching fuelled by the illegal wildlife trade. But there’s still hope for the Siamese crocodile: after more than a decade of joint conservation efforts in the Srepok Wildlife Sanctuary, researchers confirmed the discovery of hatchlings at the beginning of September 2021. It is the first-ever photographic record of a breeding population of this Critically Endangered species, showcasing what is possible to achieve when stakeholders work together in a strategic and long-term partnership. Cambodia’s Ministry of the Environment and WWF focus on the natural resource management of the Srepok and Phnom Prich Wildlife Sanctuaries via habitat and species protection, strict law enforcement efforts, monitoring, and community engagement and livelihoods support in surrounding villages.
#91 Siamese fighting fish
The Siamese fighting fish, Betta splendens, is unique not only in its beautiful colours but also in its fascinating reproductive behaviour. Before pursuing the female, the male Siamese fighting fish meticulously prepare a nest of bubbles that will provide oxygen for its developing future offspring. After chasing and finding their female mate, males fertilise the eggs, and the pair place each egg carefully into the nest. But the males’ job is not done yet – they will guard the nest until the eggs hatch, a few days later. Endemic to Thailand, this species inhabits intact marshlands in shallow zones from the Mae Khlong to Chao Phraya basins. Sadly, Siamese fighting fish populations are decreasing, mainly due to habitat degradation. Their freshwater habitats have been converted into intensive farmland and urban areas or are polluted, especially in central Thailand, which is its centre of population. They are also threatened by genetic erosion from escaped farmed stock into wild habitats. This species is very popular in the aquarium trade, being bred in many domestic variations for national and international markets.
#89 Eurasian water shrew
The Eurasian water shrew, Neomys fodiens, is one of the few venomous mammals left in the world. With its venomous saliva, this semi-aquatic species paralyses its prey. It hunts on land or in water, where they dive in and swim at a fast pace, searching for invertebrates like crustaceans and insects. Occasionally they are known to take small fish and amphibians. Even though Eurasian water shrews don’t have webbed feet, scientists believe that the stiff hairs on their back feet and tail aid swimming by propelling them in the water. They also have a thick and water-repellent fur, which protects against the cold and wet. Biologists have recently uncovered the genetic secrets of the diving behaviour of this species and its order, Eulipotyphla, which means truly fat and blind. They are the most aquatic of all European shrews, living in small holes in the banks of their watery habitats. These include many wetland habitats, including lakes, rivers, streams, marshes, and bogs. This species is solitary and highly territorial, with males only leaving their turf to search for females in the breeding season. They extend from the British Islands eastwards to Lake Baikal, Yenisei River (Russia), Tien Shan (China), and northwest Mongolia. They are also found in the Mediterranean, from northern Spain to Bulgaria. Although generally abundant and assessed as Least Concern, there are records of local population declines most likely due to wetlands loss and degradation (e.g., drainage, pollution).
#88 Yellow-bellied toad
The Yellow-bellied toad, Bombina variegata, is a rather small aquatic species with a vibrant underbelly. The bright yellow is a warning signal to predators, as this species presents toxins on their warty skin. When potential predators are around, the Yellow-bellied toad plays dead by throwing itself on the back and showing the coloured belly to the predator. As they can't stretch their tongue out of their mouth, they don't hunt flying insects. Instead, they pick up those that fall into the water or predate smaller insects and ground animals at night on land. They inhabit many types of wetlands (lakes, ponds, swamps, rivers, among others) in the uplands of Western, Eastern, and Southern Europe (Carpathian, Balkans, and Apennine mountains). Although listed as Least Concern by the IUCN Red List of Threatened Species, their last global assessment is from 2009, and their populations are locally threatened. They are listed as Critically Endangered in Germany and extinct in Belgium, mainly due to habitat loss and fragmentation. Discharge of pollutants into wetlands is also a threat, but they show signs of tolerance to slight water pollution. Yellow-bellied toads are declining steadily since the 1990s and increasing pressures on their habitats like plans to build hydropower dams in the last free-flowing glacial river in the European Alps - the Isel River in Austria – threaten theirs and freshwater biodiversity's existence.
#85 Hump-backed mahseer
The Hump-backed mahseer, Tor remadevii, is the largest of the iconic mahseer species. Endemic to the River Cauvery, this species is the most widely recognised fish in India and is worshipped as a god by the Mullukuruma people of Wayanad, Kerala. But its mythical status goes beyond India’s borders - it has lured anglers from all over the world since the 1970s. Anglers have had an important role in conserving this freshwater mega-fish. The income generated from international anglers visiting the Cauvery supported the transformation of former poachers into angling guides and river guardians, motivating them to protect the mahseer and their lucrative new income stream. Also, scientists analysed the detailed catch-log books kept by angling camps in 2015 and found that the mahseer population was in decline. This evidence supported the formal recognition of the Hump-backed mahseer as a separate species and its classification as Critically Endangered by the IUCN Red List of Threatened Species. It became possible to assess that the Hump-backed mahseer was reduced by more than 90% over three generations, mainly due to the introduction of non-native species, habitat degradation, and illegal and unsustainable exploitation. Anglers and other local and international stakeholders play a crucial role in bringing the species back from the brink of extinction. The Mahseer Trust released a cartoon story to share some insights from their long-running research and interviews with the indigenous people of Wayanad, whose rich cultural heritage respects and helps to protect the priceless Hump-backed mahseer.
#87 AMAZON KINGFISHER
Contrary to what its name might suggest, the beautiful Amazon kingfisher, Chloroceryle amazona, can be found from Mexico to Argentina. Although described in the Amazon, this species has been abundant in many regions of South America, having cultural significance and even becoming the bird-symbol of Florianópolis, a city in the South of Brazil. This petite bird species is resident (non-migratory) and inhabits rivers and the edges of ponds and lakes, favouring smaller and slow-flowing rivers and creeks. Amazon kingfishers are generally found in pairs or singly, especially when fishing. Their strong beak is specially adapted to capture fish, and they are often seen perched on a branch or rock close to water before plunging headfirst after their favourite prey. They breed by streams and build holes in ravines near the water bodies, using them for nesting. Males attract females by offering them food, and the pair can stay together for years. They look very different from each other – males have white underparts apart from a broad chestnut breast band and some green streaks on the flanks, while females’ plumages are less bright and with white underparts and green patches on the side of the chest and green flank streaks. Their population is vast but with a decreasing current trend, being listed as Least Concern by the IUCN List of Threatened Species.
#86 giant river prawn
The Giant river prawn, Macrobrachium rosenbergii, is the largest member of the Macrobrachium genus, which means “big arm”. This freshwater species can live up to approximately three years. It depends on brackish water on larval stage, inhabiting coastal rivers and estuaries. Found in Southeast Asia, its natural range extends from Pakistan up to Borneo and Java. It is a food source in subtropical and tropical regions and one of the most economically valued freshwater prawn species for aquaculture, representing 3% of total global crustacean production in 2016. Although this river giant is extensively fished, it is listed as Least Concern by the IUCN Red List of Threatened Species due to its wide natural range, likely overlapping with protected areas. However, aquaculture can bring risks to non-native habitats when species like the Giant river prawn “escape” and start successfully breeding populations. There are widespread reports of Giant river prawns establishing populations, but up to this point, it is not known if these invasions have had any negative impacts.
#84 Zebra catfish
Brazil's dazzling Zebra catfish, Hypancistrus zebra, is endemic to a small portion of the Xingu River, a tributary of the Amazon. Due to its attractive black and white stripes, Zebra catfishes are highly sought for the aquarium trade where they are better known as Zebra plecos, and it was exported from Brazil in great numbers for years. But it was caught and sold at such an unsustainable rate that the government banned its export and added the Zebra Catfish to the Brazilian Red List of Threatened Species in 2004. The last assessment from 2014 places this species as Critically Endangered. In 2016, Brazil proposed H. zebra at the CITES conference for protection under Appendix III. However, this Appendix doesn't impose a complete trade ban or affect interstate trade within a country. In addition, the ongoing ban has led to a thriving black market, even though the Brazilian government aimed to reduce ongoing smuggling via neighbouring countries. To make matters even worse, the only freshwater habitat of this species is under pressure from hydropower dams. Contradicting some of its own efforts to save the Zebra Catfish, the government greenlighted the construction and operation of the controversial Belo Monte hydropower dam in the Xingu River. The dam's presence is already showing some negative effects in the region, such as a drop in water levels. H. zebra is now bred in large quantities in high-tech facilities in Asia. But without urgent action, this and many other fishes will be those born and raised in aquaria.
#83 Rogue mushroom
This fungi species seems to have gone “rogue" – it's the only reported aquatic gilled mushroom! More than 600 known freshwater fungi are known, but they are usually microscopic and do not produce visible fruiting bodies like mushrooms. It is very rare to find members of the Basidiomycetes that can grow underwater, especially submerged and truly gilled mushrooms. During a family picnic in 2005, hydrologist and professor Robert Coffan from Southern Oregon University discovered this intriguing species in the Rogue River in Oregon. Prof. Coffan reached out to colleagues (mycologists), and five years later, the Rogue mushroom was described as a new species as researchers confirmed this species' unique DNA fingerprint. But there's still much to learn. P.aquatica breaks down dead organic plant matter and usually grows on wood as a substrate. But scientists are still investigating how this species breathes and releases its spores to reproduce, as all the other gilled mushrooms do it through the air. One of the hypotheses is that in addition to buoyantly stabilizing P.aquatica underwater, the large gas bubble trapped under the mushroom cap provides a chamber wherein spores eject. But then spores could flow downstream to the ocean, leading to another hypothesis that aquatic insects could be dispersing them as their larvae have been observed grazing and filter-feeding on the mushroom. The bubble could also function as a type of external lung, facilitating oxygen exchange. The Rogue river is notoriously highly oxygenated, which may limit the mushrooms’ distribution; so far, only two populations have been found.
#81 Large red damsel
The Large red damsel, Pyrrhosoma nymphula, is one of the most common damselflies in Europe’s wetlands. But be aware, they are very similar to another species: the Small red damselfly, which is less red. Large red damsel males are bright red with a black thorax, but females can be almost entirely black. Most likely, you will see the active and robust Large red damsel flying over or near slow-ﬂowing and standing waters. However, in eastern and northern Europe, where it is less common, it mostly reproduces at running waters. They also have smaller numbers in north Morocco, northern Tunisia, and the mountains of Southwest Asia. They like breeding mainly in a wide variety of wetlands, from acidic bog pools to brackish ditches, especially sheltered waters with abundant aquatic plants. Their aquatic nymphs (or naiads) have elongated abdomens that terminate in three leaf-shaped tracheal gills. These fascinating gills can absorb dissolved oxygen from water and function as ﬁns during the undulating swim of the larvae. Damselfly nymphs tend to stay for one year underwater. When it’s time to emerge, they crawl onto the shore or cling to an emergent aquatic plant and shed into adults. Shed skins are a common sight on waterside vegetation, especially for Large red damselflies, as most adults emerge from the pond at the same time over a short period in the spring.
#82 Cuban gar
Also known as Manjuarí, the Cuban gar, Atractosteus tristoechus, is the rarest of all the seven known gar species. The gar family is quite unique - their eggs are toxic (to mammals, birds, and most arthropods, but not fishes!), and their lineage dates back to the dinosaurs’ age like the Sturgeons. Endemic to Cuba and the nearby Isle of Youth, the Manjuarí can grow up to two meters long. It lives in shallow streams, swamps, crystal-clear springs, and cascading waterfalls. This species is the most understudied gar and the most threatened. Assessed as Critically Endangered by the IUCN Red List of Threatened Species, Cuban gars’ declining populations face threats associated with introducing invasive species, habitat loss and alteration, and overfishing of prey items. A recent assessment shows that Cuban gars share their home with other 79 species of freshwater fishes, of which 54 are endemic to the two largest islands, Cuba and Hispaniola. It also revealed that 45% are threatened with extinction. The arrival of invasive species like the African Catfish, Clarias gariepinus, resulted in the steep population declines of the Manjuarí. As apex predators of some freshwater ecosystems such as the Zapata Swamp - the largest wetland in the Caribbean - Cuban gars support the presence and endurance of other native fish populations. Hence, the Manjuarí is a crucial species for conservation efforts, as it is a key species for maintaining their ecosystems’ health.
#79 Maripano piranha
Pristobrycon careospinus is a rare piranha locally called Maripano by the Piaroa ethnic group in Venezuela. The rare photo - actually the first live pictures of this species! - was taken by the Photographer Ivan Mokolji, who explains how he managed such a difficult task on this great article. Found in the Atabapo river in the Orinoco basin, this species is part of the Serrasalmidae fish family - piranhas and pacus. Serralmids are keystone ecological taxa - some species are top riverine predators and/or primary seed dispersers in the flooded forest. Piranhas are notoriously famous for their ferocity, mainly due to feeding on corpses and nipping bathers to defend their nests. While piranhas are indeed generally carnivorous, some species like the Maripano are facultative frugivores: they can eat both other animals (e.g., insects and fish) as well as fruits, seeds, and leaves. Despite their keystone status and commercial significance throughout South America's Amazon, the ecology of piranhas and pacus are poorly understood. Pristobrycon careospinus is known from only the original description with a single specimen captured in 1974. Hence, records such as Mokolji's are essential for freshwater biodiversity assessments and conservation.
The gharial, Gavialis gangeticus, is a specialist fish-eating river crocodilian generally about 3 meters long, but some may reach more than 6 meters. With seasonal migratory behaviours and social hierarchies, gharials come together for mating and nesting during the dry season in the highly seasonal, monsoonal rivers in which they live. On the sandbars and river banks, females lay an average of 40 eggs in a hole nest, and for 1 to 2 months, they will look out for them typically together with one single large male. The females open the nests at the time of hatching, and hatchlings from multiple nests aggregate in “crèches,” numbering from hundreds to a thousand or more. Once the monsoon waters start to rise, adults migrate while the hatchlings disperse widely into the aquatic shorelines. Gharials were once very common and abundant in the main rivers and tributaries of the Indus, Gangetic, and Brahmaputra-Meghna Basins. Sadly, they are currently only found in India, Bangladesh, and Nepal and are regionally extinct in Pakistan, Myanmar, and Bhutan. According to IUCN, gharials are Critically Endangered mainly due to dams and barrages which disrupt river flows , mortality in fishing nets, and historical and unregulated hunting for their skin. Nowadays, threats also include sand mining and boulder removal. WWF-India conservation efforts include a gharial reintroduction programme in India in collaboration with the Uttar Pradesh Forest Department. WWF-Nepal started a Gharial Conservation Action Plan for Nepal in 2018.
#80 Cape pondweed
Cape pondweed, Aponogeton distachyos, is an aquatic flowering plant endemic to Western Cape in South Africa. This species produces floating leaves and flowers from stems growing at the bottom of water bodies, where it’s rooted. Typically blooming in small ponds from fall to spring, its flowers are known to be vanilla-scented and often visited by pollinators like bees. Humans also appreciate their flowers – it’s a delicacy in South Africa where they are commercially grown for their edible roots, stems, and flowers. This species is present in traditional dishes, where the flowers and leaves work as replacements for cabbage in stews and young shoots as an alternative to spinach or asparagus. It is also used for traditional medicines, the stems as a soothing treatment to reduce redness from burns and wounds, and together with flower petals for acne treatment. Due to its attractive flowers, it is also an ornamental plant. Sadly, such a feature has also led to the introduction of this species in other parts of the world. Invasions of non-native species are a threat to the economy and can cause systemic ecological damage. In freshwater ecosystems, invasions are occurring at a fast pace, and their impacts are enhanced by increased nutrient levels, loss of top predators, and altered flow regimes.
#76 Amazonian Manatee
The Amazonian manatee, Trichechus inunguis, is the only manatee to occur exclusively in freshwaters. It is also the smallest and most slender member of the manatee family, distinguished by smooth rubbery skin and large flippers lacking nails. Endemic to the Amazon Basin, its range unevenly covers over an estimated 7 million km2 – from the headwaters in Colombia, throughout Ecuador, Peru until the Amazon’s mouth in Brazil. They prefer murky and calm waters away from human settlements. As herbivores, they feed on a large quantity (8-15% of their body weight daily) of aquatic and semi-aquatic vegetation during the rainy season. All food is stored up as fat, supplying them during the dry season - when the water levels start to drop, individuals migrate from the flooded areas to deeper water bodies with less available food. On the other hand, they are less vulnerable to hunting and predators. Females are very attentive mothers, teaching the young to swim, select plants to graze, and surface to breathe. Due to this process, she will only produce offspring once every four years. Listed as Vulnerable on the IUCN Red List of Threatened Species and decreasing numbers, this species is threatened mainly by historical and current hunting, especially for its meat. Entanglement in fishing nets and habitat alterations (e.g., pollution and dams) are also threats. Data is limited due to their secretive behaviour, which hinders monitoring and conservation strategies. Conservation efforts by WWF in the region include monitoring projects via drones and satellites. In Peru, WWF has recently worked with Prodelphinus to support the government in building the National Action Plan for the Conservation of River Dolphins and Amazonian Manatee approved in 2018.
#74 Titicaca water frog
Meet one of the world’s largest exclusively aquatic frogs: the Titicaca Water Frog, Telmatobius coleus. Endemic to Lake Titicaca in Peru and Bolivia, this species spends its entire life underwater. Found at depths of up to 100m, Scientists believe Titicaca water frogs can breathe through their loose-fitting skin, which performs all gas exchange. Listed as Critically Endangered on the IUCN Red List of Threatened Species, this species population has declined dramatically recently due to harvesting for human consumption, degradation of its habitat (e.g., pollution from mining and agriculture), and water extraction. Its larvae are also thought to be predated by introduced non-native trout species. Humans harvest the Titicaca water frog for food and traditional medicine, being used as an aphrodisiac and treatment for memory loss and asthma, among others. In 2016, 10,000 Titicaca water frogs were found dead along the Coata River, one of the Lake’s tributaries, probably due to the river’s pollution. Although the Lake is under habitat management and protection, further action and better enforcement are needed. Recently, two dozen women – artisans who used to poach these frogs – started knitting frog toys and finger puppets to help protect the frog and the environment with the support of the Denver Zoo.
#77 Freshwater pufferfish
Pufferfishes are also in freshwaters – meet the Freshwater pufferfish, Tetraodon mbu. Freshwater pufferfishes inhabit large rivers and lakes, feeding mainly on molluscs and insects. This species is widely distributed in the Congo river basin, besides living in the delta and lower Malagarasi River in Tanzania. In this restricted range, it is listed as Vulnerable by the IUCN Red List of Threatened Species due to increased agriculture and land-use change. Overall, their population trend is unknown, and conservation efforts would benefit from research and monitoring of the Congo basin. Pufferfishes present many fascinating features, one of the best known being their defensive behaviour against predation in which they inflate their bodies, looking like a colourful floating balloon. By swallowing water, they can reach a volume almost four times their average size. They are also among the most poisonous fish in the world – they have potent neurotoxins, which can cause fatal human intoxication. Some freshwater puffer species present a high level of toxins on their skin, but further studies on the Tetraodon mbu are necessary to give us a clearer picture.
#75 Dumbéa River pipefish
Freshwaters also have beautiful colourful pipefishes - meet the Dumbéa river pipefish, Microphis cruentus, endemic to New Caledonia. Closely related to seahorses, freshwater pipefishes mainly inhabit tropical and temperate seas. But there are a few species in the Indo-Australian Archipelago restricted to freshwater, such as the Dumbéa river pipefish. Known from the lower reaches of the Dumbéa River, this species likely feeds on small benthic and planktonic animals like insect larvae and crustaceans. Similar to other pipefishes, Dumbéa females deposit their eggs underneath the male's trunk or tail. And the male is the one that does the work of incubating them for several weeks in either partly or wholly concealed pouch. Not much is known about this species, being listed as Data Deficient by the IUCN Red List of Threatened Species. Recently, Shoal - an organisation dedicated to conserving freshwater species – launched the Search for the Lost Fishes campaign. They considered adding this species to the Top 10 Most Wanted species, as it hadn't been seen for a decade - or so they thought. Glady, thanks to the naturalist Damien Brouste, who recorded the Dumbéa on the citizen science and naturalist platform iNaturalist, Shoal discovered that this species wasn't a lost fish.
#73 Moss animal
Cristatella mucedo is a small freshwater invertebrate which is part of Bryozoa phylum, sometimes known as moss animals. C. mucedo has a wide range and is distributed across America, England, Norway, Poland, New Zealand, and likely many other places. As they are not as well studied as other species and we still have lots to learn about these bryozoans. This species likes stiller waters such as lakes, ponds, and slow flowing streams and rivers and is generally found up to 2m in depth. It grows on submerged substrates as colonies of genetically identical individuals called zooids. Each zooid is about 2 mm long and has a horseshoe crown with 80-100 ciliated tentacles, which it uses to capture and filter organic particles. Zooids form clear, soft, gelatinous colonies resembling a caterpillar. Most bryozoan colonies are strictly sessile, but C. mucedo is somewhat mobile – it moves a few cm/day by sliding, and scientists presume that a thin fluid secreted by its cells helps them glide. But it may be that muscles in the colony bottom wall also play a role. They are primarily asexual and reproduce via small encapsulated structures called statoblasts, which potentially form new colonies. Water currents, wind, and animals like fish and aquatic birds disperse the statoblasts. This tiny invertebrate generally does not like polluted waters, and its presence indicates good water quality.
#72 Giant South American river turtle
Podocnemis expansa, the Giant South American river turtle, is one of the biggest freshwater turtles of South America, reaching over 80 cm in shell length and 65kg in mass. This impressive species used to be abundant in most rivers of the Amazon and Orinoco basins, occurring across eight countries. They would migrate by the thousands up rivers to nest collectively on high sandbars, including hatchlings that tag along with the adults to feeding areas sometimes many miles away. The hatchlings and females are able to communicate with each other through underwater vocalizations. Although the freshwater giant is currently listed as Lower Risk/ Conservation Dependent by the IUCN Red List of Threatened Species, the IUCN Tortoise and Freshwater Turtle Specialist Group (TFTSG) recently recommended the categorization change to Critically Endangered. Giant South American river turtles are historically a valuable source of food and income, especially in riverine communities. Large-scale commercialization only started after Europeans arrived in the region, leading to the overexploitation of eggs and meat for consumption and oil extraction. These threats have decimated populations of this river turtle across its range. The construction of mega-dams is also an issue, hindering its recovery. Long-term conservation efforts by the Brazilian Government and other institutions led to the stabilization of some populations through the protection of areas (reserves) and the release of huge numbers of hatchlings from protected nests. However, to increase their number to viable populations, best practices should include protecting the entire river basin, besides improving monitoring and enforcement.
#71 Lister's river snail
The charming Viviparus contectus is part of a family of river snails – the Viviparidae. The family name is due to their ovoviviparity: they bear live young - their offspring hatch from the eggs inside the female's body. As a gilled snail, Lister's river snail can breathe underwater - it allows water to enter the shell and go through its gills to obtain dissolved oxygen. Due to this ability, they are also able to filter water like mussels. This trait is important in polluted waters, where increasing temperatures combined with rising nutrient inputs tend to intensify eutrophication symptoms. V. contectus feeds on organic particles and microbes and lives in large slow-flowing rivers, large drainage ditches, fenland dykes, ditches on grazing marshes, and large ponds and lakes. This species is widespread in many countries in the Palearctic region, but there are considerable gaps in the taxonomy. They can host different groups of parasites, including those of medical importance. This species has been used as a traditional medicine in Korea and China for liver diseases and alcohol poisoning. The latter country also uses it as a food supplement since it contains high amounts of protein, essential amino acids, taurine, calcium, iron, and zinc. This freshwater snail is also part of the aquarium trade, but the main known threats are pollution and habitat loss. They are listed as Least Concern by the IUCN Red List of Threatened Species and with a decreasing population trend.
#70 White-throated Dipper
The White-throated dipper, Cinclus cinclus, is one of the few riverine songbirds worldwide. Found widely across Eurasia, this territorial bird likes fast-flowing, clear-water rocky streams, and rivers with abundant freshwater invertebrate prey. It also uses glacial lakes and shallow watercourses - their freshwater habitat has to have riffles and exposed rocks for breeding. They set their large globular nests made of moss and dry leaves on rock crevice or cliff ledge, sometimes even behind waterfalls, but almost invariably over running water. Mostly found in uplands, this species is resident but does some post-breeding movement to more lowland rivers or sometimes to the coast. It's fascinating to see them in the wild – they are often bobbing when standing, as they are dancing to some unheard music. They generally plunge into the water to feed and they can also submerge completely! They can swim against the current by walking on the river bottom, using their wings to stabilize themselves as water flows over them. Listed as Least Concern by the IUCN Red List of Threatened Species, they are not globally threatened, but their populations are decreasing mainly due to pollution. White-throated dippers are widely recognized as environmental indicators - their status and abundance strongly reflect the water quality and rivers' habitat structure.
#69 fishing cat
Not all cats dislike water – the Fishing cat, Prionailurus viverrinus, is strongly associated with wetlands and, as its name implies, it often enters the water to fish. Their exceptional dietary choice among felids suggests even some morphological adaptations such as semi-retractile claws that can grip slippery aquatic prey and a double-coated fur, which prevents the body from getting wet. But this nocturnal and elusive cat also preys on frogs, crustaceans, snakes, birds, and scavenges on carcasses of larger animals. About twice the size of a typical house cat, this species preferred habitat is wetlands, which destruction and degradation have led to its populations' decline. Listed as Vulnerable by the IUCN Red List of Threatened Species due to threats such habitat loss (from urban encroachment) and other threats such as wetland drainage for agriculture, pollution, and logging, which has lead to the eradication of Fishing cats from much of their previous range across South and Southeast Asia. Since 1970, the world has lost approximately 87% of its wetlands, and those remaining are disappearing three times faster than forests. A healthy population of fishing cats, and their prey, can only be sustained in a healthy environment. Learn more with this great read.
#68 Freshwater pearl mussel
The Freshwater pearl mussel, Margaritifera margaritifera, can often live for more than a century, even two! In Sweden, scientists recently discovered the oldest known specimen, which is 280 years old. They have a complex life cycle, which depends on salmonid fish exclusively. Males release sperm into the water, and the female inhales it to fertilize its eggs. Within its gills, the female pearl mussel broods the eggs developing into microscopic larvae called glochidia. When the temperature starts to rise during summer, it releases the glochidia as a stress response. The timing is perfect - it coincides with the presence of salmonids, so the 4 to 60 million glochidia can find a fish to be their host. Just as the fish takes in water to pass over its gills to breathe, the glochidia snap into the fish’s gills. As a defence mechanism, the fish creates a cyst around the glochidia. They stay until the following spring or summer when they are juveniles, dropping off the fish into the river’s gravel, where they become adults. Found in North America, Europe, and Siberia, this species is listed as Endangered by the IUCN Red List of Threatened Species. Their populations are declining due to pollution, river regulation, and habitat degradation including dams, which also affect salmonid populations. Their conservation benefits the entire riverine ecosystem - they are excellent indicators of ecosystem health and filter up to 50 L of water a day, improving water quality.
#67 Afia Birago's puddle Frog
The Afia Birago's puddle Frog, Phrynobatrachus afiabirago, is named after the mother of Ghana's first formally trained herpetologist, Dr. Caleb Ofori-Boateng. Dr. Caleb discovered the endemic puddle frog in the Atewa Forest's swampy habitats in Ghana – a unique area of mountain forest-like vegetation in West Africa. This puddle frog likes large forest ponds and swamps, presumably breeding in the water. Its population inhabits only two known sites, and it's likely to be decreasing due to the ongoing decline of the extent and quality of their habitats. In 2016, a wave of bushfires destroyed most of the forest habitat close to one of the frog's ponds. Listed as Critically Endangered by the IUCN Red List of Threatened Species in 2019, Afia Birago's puddle frogs face threats such as ongoing illegal logging, artisanal mining, and farming. Scientists estimate that 80% of the already small population will disappear in the next ten years if bauxite mining plans in the Atewa Forest Reserve move forward. Dr. Caleb and many environmental Civil Society Organizations argue that mining in that region would be catastrophic to biodiversity and human health as Atewa is the water source for over five million people. Finding the endemic frog secured Atewa Forest Reserve's designation as an Alliance for Zero Extinction site, restricting mining as an activity in this habitat which is already a Key Biodiversity Area. Also, together with Synchronicity Earth, Dr. Caleb started an amphibian monitoring programme in the region.
#65 Splashing tetra
The Splashing tetra, Copella arnoldi, is an extraordinary fish species – it lays its eggs on land! At the water's surface, females and males lineup side by side and jump together out of the water to spawn. Females lay their eggs on hanging leaves, and males fertilize them immediately. The male is then tasked with keeping the eggs moist by splashing them with its tail for around three days until they hatch and fry fall into the water. The unique breeding behaviour and parental care can be seen in the Orinoco and Amazon rivers in South America - this species native range. They have high commercial importance as ornamental fish in the region. According to the Brazilian Red List of Threatened Species, the Splashing tetra is listed as Least Concerned. However, the last assessment was made in 2014, and their freshwater habitat is under pressure mainly from hydropower dams.
#66 Russian sturgeon
The Russian sturgeon, Acipenser gueldenstaedtii, was once widely distributed in the Danube river. Now, it is listed as Critically Endangered by the IUCN Red List of Threatened Species, and it is the most endangered sturgeon species of the four that still exist in the Danube river. This species likes to swim in deep parts of large rivers, spawning on stone or gravel bottom in areas of strong currents. They would migrate a considerable distance upstream before spawning, going as far as Bratislava. Most of their spawning sites have been lost due to dam constructions, except in the lower Danube river. But this species also faces other huge threats in one of their last safe reproductive harbors: illegal poaching and trade. A new WWF market survey found that one-third of sturgeon caviar and meat products were sold illegally in the lower Danube region. Out of 27 samples from poached sturgeons, 22% were from Russian sturgeon – a very high amount considering the extreme scarcity of this species in the wild. Stopping the illegal trade is one of the key pillars of WWF’s global Sturgeon initiative. In 2019, WWF Bulgaria released thousands of farmed young Russian sturgeons into the Danube. But that is not enough to ensure their protection. WWF’s conservation efforts also include reducing pressure on their remaining populations by addressing poaching and ensuring their freshwater habitats are healthy.
#64 Green hydra
The Green hydra, Hydra viridissima, is a freshwater species of cnidaria – a “relative” of the jellyfish. Green hydras are no more than 3 cm long and green due to the presence of symbiotic Chlorella, algae known to provide a significant nutrition source to cnidarians. Found at depths from shallow waters to 60m, Green hydras are widely distributed throughout the world’s ponds, rivers, and slow-flowing parts of streams and rivers. These tiny hydras are solitary polyps without the medusae phase, and their bodies only have two layers of cells. Still, they have regenerating capabilities - when subjected to pressures in the environment, they may lose body parts like their tentacles and later build them back up. Some scientists believe that they might even live forever under the right conditions – in the wild, they face disease, predators, and water contamination. Research shows that they don’t show any signs of deteriorating with age, unlike most multicellular species. They are sensitive environmental indicators and play an essential role in freshwater food webs, especially as predators when abundant. Green hydras use their tentacles to catch prey, which has stinging cells called cnidocytes that immobilizes it. Curiously, hydras only have a mouth when it’s time to feed – their mouth is not a permanent opening, vanishing after feeding. Between the ring of tentacles, a small mound called hypostome has a group of cells morphologically distinct. To open and close its mouth, these cells change shape, becoming longer and narrower to widen the gap and returning to their original form to close it – a similar process to when the pupils in your eyes dilate and constrict.
#63 Singapore freshwater crab
Singapore freshwater crabs, Johora singaporensis, are smaller than the size of a thumb, growing 2 to 3 cm. Endemic to Singapore’s freshwater habitats, this species hides under rocks along river edges and inside clumps of leaves and detritus. They feed on plant detritus and oligochaete worms present in the soft stream's mud. Listed as Critically Endangered by the IUCN Red List of Threatened Species, this species is sadly among the world's most threatened species. They prefer relatively clean and fast-flowing streams in the highlands, which are at higher risk due to habitat loss and habitat acidification. Conservation efforts include measures to increase this species' wild populations, led by the Freshwater Crab Working Group in Singapore. NParks (National Parks Board) of Singapore has successfully hatched more than 150 crablets in captivity and has begun to release these captive-born individuals into the wild. In 2018, in partnership with Singapore’s National Parks Board (NParks), WWF highlighted 10 threatened species in Singapore currently under active conservation, including the tiny Singapore freshwater crab.
#61 Freshwater sponge
Spongilla lacustris is one of the 248 known freshwater sponge species occurring globally. S. lacustris is the most common and widespread freshwater sponge species and the most abundant in Central Europe. It lives in rivers and preferably lakes, often growing attached under rocks or logs. Its colour is mostly white, but it can look greenish due to symbiotic algae. Freshwater sponges are subject to harsh environmental conditions, having developed a dormancy mechanism. When exposed to excessive cold or harsh situations, they form highly resistant gemmules that remain viable after the other part of the sponge dies. Once conditions improve, the gemmules germinate into a new sponge. These ancient invertebrates are sessile (fixed in one place) and filter water to feed on small aquatic organisms like protozoa, bacteria, and other free-floating life. A ﬁnger-sized specimen of S. lacustris can ﬁlter more than 125 l of water in a day. They are prey to ducks, crayfish, and various macro-invertebrates. Sponges play a key role in recycling organic matter and contribute to the primary productivity of freshwater ecosystems. Their presence in an ecosystem can be an indicator of good water quality.
#62 Baikal seal
Baikal seals, Pusa sibirica, are one of the few species of seal restricted to freshwater. Located near the Mongolian border in southern Siberia, Russia, Lake Baikal is the oldest (25 million years) and deepest (1,700 m) lake in the world, containing 20% of the world's total unfrozen freshwater reserves. These freshwater seals are mostly confined to the lake, although they travel short distances into rivers flowing into and out of the lake. They are amongst the smallest of the seals (ranging between 1.1-1.4 m and weights of 50 to 130 kg), and may have the greatest longevity. Approximately 10% of the population is over 20 years old - with records of males reaching 52 and females 56 - and they continue to produce pups until they are 43-45 years old. During winter, they are mostly solitary and spend much time in the deep water under the ice, making and maintaining breathing holes to allow them to feed. Females with pups or that are pregnant are more likely to be on the ice, building dens to protect their offspring from predators. Baikal seals generally dive for a couple of minutes, but they can dive for longer - the longest recorded dives were over 40 minutes during winter. They are threatened by contamination from organic pollutants coming from the growing industrial activity in the Baikal watershed.
Native to the Amazon, the Arapaima, Arapaima gigas, is one of the largest freshwater fish globally - it can grow up to 3m, but nowadays it’s rare to find a specimen more than 2m long. Its Brazilian name, 'Pirarucu,' comes from two indigenous words – pira means fish and urucum means red, referring to the reddish marks towards the tail-end. During the mating season, males' red colours become more intense. After pairing, males clean the river bed with their jaws by pulling out any weeds or obstacles in a selected area, where they dig a puddle for the female to lay its eggs and fertilize them. The female stays nearby during the incubation period, while the male circles a bit further to scare off any predators. Arapaimas have gills and a modified respiratory swim bladder which works like a lung – they need to return to the surface every 20 min to breathe air, making them easy to catch. They are economically and culturally important to many traditional communities. Climate change effects, habitat degradation, and increased demand on fish stocks put the Arapaima and livelihoods at risk. Local communities are leading the management and conservation of their resources with the support of the government and multiple organizations, including WWF. Check this video to see what local fishers say about the Arapaima and WWF-Brazil's work to support them. Learn more about this and other valuable freshwater fishes with The World's Forgotten Fishes report.
The Piraiba, Brachyplatystoma filamentosum, lives mostly on the soft-bottom floor of the Amazon & Orinoco rivers. The Piraiba is one of the 11,000 species of migratory fish, with records of maximum distance travelled as far as 7000 km. Juveniles float downstream where they grow rapidly. Once they reach adulthood, they migrate upstream to spawn. Due to this migratory behaviour, artificial barriers like dams can obstruct the “pathway” and reduce their ability to complete their life cycle (Learn more about migratory fish with the Living Planet Index For Migratory Freshwater Fish). The Piraiba is an essential environmental, social, and economic resource in the South American basins, and it is threatened by over-harvesting. Hence, it is imperative to conserve this species, its fishery, and its rivers - learn more about this and other beautiful important fishes with the World's Forgotten Fishes report. And check out this video to see the Piraiba swimming.
#58 Asian water monitor
Meet the largest aquatic lizard and the world’s second largest-lizard - the Asian water monitor, Varanus salvator, which can reach more than 3 m in length and 25kg. No lizards are strictly aquatic, but this semi-aquatic and opportunistic species lives in various water systems; mangroves, swamps, and wetlands at altitudes below 1,000m are its most important habitats. Frequently seen on river banks and swamps, this amphibious species can dive underwater to forage and/or to escape predators. They are remarkably widespread throughout southern and Southeast Asia – researchers believe their extensive distribution and adaptability could be due to their ability to swim and cross large stretches of water and their generalist diet. Asian water monitors will eat about any animal they think they can consume - fish, juvenile crocodiles, tortoise - there are even records of them scavenging human corpses! Regularly harvested and traded as a pet and for their meat, skin, and medicinal value, this species is the most intensely traded lizard species worldwide. Between 2010-2018, the two major source countries, Malaysia and Indonesia, exported more than 2.3 million skins of wild-caught specimens, mainly for the fashion industry. It is listed as Least Concern by the IUCN Red List of Threatened Species, but their population trend is unknown (last assessed in 2009).
#56 Dalmatian Pelican
The Dalmatian pelican, Pelecanus crispus, is one of the biggest birds in the world and the largest of the pelican family, ranging from 1,60 to 1,80m. This huge pelican feeds mostly on fish and is widely distributed – it occurs mainly in wetlands, where it breeds in fragmented ranges from eastern Europe to east-central Asia. It nests amongst aquatic vegetation on floating or stationary islands isolated from the mainland, avoiding mammalian predators. Dalmatian pelicans are dispersive in Europe and migratory in Asia. When migrating, large lakes and wetlands form important stop-over sites. Their population suffered massive declines in the past, mainly due to wetland drainage and fishers' persecution. Disturbance from tourists, wetland alteration and destruction, water pollution are among other continuing threats. However, Thanks to conservation measures, populations increased in Europe, being downlisted from Vulnerable to Near Threatened by the IUCN Red List of Threatened Species. Nevertheless, as this species currently presents a decreasing population trend and the ongoing threats in much of their breeding and migratory range, conservation efforts must continue. The Dalmatian pelican is one of WWF’s Asian Flyways Initiative priority species. One of the aims of the Initiative is to improve ecological connectivity in the flight path of this and other migratory bird species.
#55 Diving bell spider
The Diving bell spider, Argyroneta aquatica, is the only spider to live underwater for most of its life. This Eurasian species inhabits eutrophic lakes, ponds, marshes, swamps, and slow-moving streams. To breathe underwater, their posterior body part called opisthosome is covered by fine hairs that trap air, being covered by a silvery envelope when they dive. They use plants from the dense aquatic vegetation to anchor their underwater silk webs. With their tiny body hairs, they collect air from the surface and release it in the web, creating an air-filled bubble - the ‘diving bell’, where the air is held by the surface tension between the silk fibres. The diving-bell works as an air deposit and as a physical gill - it absorbs dissolved oxygen from the water to meet the spiders’ metabolic oxygen requirements. They also use the bell to feed - after capturing the prey (generally aquatic invertebrates and small fish) by injecting venom into its body with their chelicerae (fangs), they carry it to the bell to consume it. Females use the bell to lay their eggs – they place an egg-filled cocoon in the upper region and lay on it for protection until hatching. The offspring only leave the bell once they have developed the fine hairs to build their first tiny diving bell.
#57 LOWLAND TAPIR
The Lowland tapir, Tapirus terrestris, has a wide geographic range - from northcentral Colombia and east of the Andes, throughout most of tropical South America. Mostly found in the tropical lowland forests and wetlands of South America, they are often seen close to water which they use as a refuge against predators as well as a place to forage or cool off. This species is known for being a strong swimmer - able to cross rivers and even dive to feed on aquatic plants. Lowland tapirs can reach the size of a small pony, growing up to 1.8m and 225kg. They are primarily solitary, using their large teeth to grind up plants, fruits, and seeds at night and resting or hiding during the day. This species is listed as Vulnerable on the IUCN Red List of Threatened Species. Main threats to this species are habitat loss due to deforestation, hunting for meat, and competition with livestock. Due to their long gestation period and generational time, tapirs are more ecologically prone to impact from prolonged hunting activity, making population recovery more difficult.
#53 Arafura File Snake
The Arafura File snake, Acrochordus arafurae, is one of the 153 known species of freshwater snakes globally. You can find this species in northern Australia and Papua New Guinea - swimming in rivers, lakes, lagoons, floodplains and their associated wetlands. The Arafura is adapted to freshwater life, being considered an entirely aquatic snake – they forage in water and cannot survive without aquatic prey. Arafura File snakes are nocturnal and non-venomous. They feed exclusively on fish, which they immobilize by constriction - as they are agile and their skin flexible (not bendy) they can easily capture and hold onto their fish prey. They have nostrils on top of their head so they can breathe whilst underwater. Listed as Least Concern by the IUCN Red List of Threatened Species, this species populations viability depends on their freshwater ecosystems health.
#54 Giant floating fern
The Giant floating fern, Salvinia molesta, is a free-floating perennial aquatic plant adapted to stagnant or slightly flowing freshwater systems. Sadly, even though this species is native to south-eastern Brazil, humans have spread it in almost all tropical-subtropical regions, becoming problematic in many areas (southern USA, Australia, South-East Asia, the Paciﬁc and south, central and eastern Africa). But floating species like those belonging to the Salvinia genus possess unique features that fascinate scientists and boost innovations. Their leaves present a "superhydrophobic" (i.e., extremely water repellent) behaviour - when immersed, the leaves wrap themselves in an air jacket and remain fully dry. Salvinia's surface also has an affinity for oil, which is, in a way, a drawback of super-hydrophobia. Such features have inspired studies in Biomimetics. Dr. Wilhelm Barthlott, Professor Emeritus at the University of Bonn, created a textile prototype based on Salvinia's properties to efficiently remove oil films from the water's surface without using chemicals or external energy supply (check out this video).
#52 Common hippopotamus
The Common hippopotamus or hippo, Hippopotamus amphibious, is a well-known mammal restricted to the rivers, lakes, and wetlands of sub-Saharan Africa. Hippos love water – as their name suggests, they have an amphibious lifestyle. They spend the day mostly in the water and in groups - herds range from the tens to a hundred – only emerging at night to feed on grass and fallen fruit. Due to their dry skin, Common hippos rely on water sources to remain moist and cool. With their eyes and ears on the top of their heads, they can watch for predators while lying low in the water. They are the only mammals known to produce an amphibious call – their loud vocalization can be transmitted simultaneously through land and water. Hippos fight for territory can be brutal, in which they use their huge ivory canines. Smaller conflicts, however, are generally settled by threat displays like the famous "yawn". Listed as Vulnerable by the IUCN Red List of Threatened Species, hippos’ wild populations have decreased 30% in the last decade, and some are regionally extinct. Losing hippos could have devastating consequences for African freshwater ecosystems, as they play a key role in transporting nutrients between the land they graze and the water in which they defecate. The main threats hippos face are habitat loss and degradation and illegal and unregulated hunting for meat and their ivory teeth. They are also threatened by drought, like in the Mara River basin, shown in WWF’s report and its consequences to biodiversity highlighted in this article with WWF’s William Ojwang as an interviewee. WF Hong Kong is also working on hippos conservation, as Hong Kong is the single-biggest buyer of hippos’ valuable teeth. WWF is shedding some light on this issue by raising awareness and advocacy (read this great blog from WWF’s Thomas Gomersall to know more).
The Taimen, Hucho taimen, is the largest salmonid in the world - reaching lengths up to two metres. But size is not their only remarkable feature - they are top predatory species known for hunting prey in packs, earning them the nickname “River Wolves”. They also have a peculiar diet, which mostly includes fish, but also the occasional rodent and bird. Unlike many salmonids, this migratory fish is potamodromous – it spends its whole life in freshwater, in large, cold, and swift-flowing rivers, traveling upstream to smaller tributaries to spawn. But it takes time for them to grow up – Taimens take up to seven years to reach sexual maturity, and they can live for more than 30 years. This species occurs in Europe and Asia, including parts of the Caspian and Arctic drainages in Eurasia and portions of the Pacific drainage in Mongolia, Russia, and China. However, this species’ numbers decreased from much of their range, being listed as Vulnerable on the IUCN Red List of Threatened Species. Due to threats such as pollution, habitat loss, damming, and climate change, this species suffered substantial (50%) population declines since 1985. Significant populations remain only in Russia and Mongolia. Mongolia harbours part of the core habitat of one of the last healthy taimen populations in the world. These populations are primarily threatened by fishing due to the high levels of unregulated, illegal practices throughout the country. The Mongolian government has taken significant action since 2012 with protective legislation. Together with other NGOs, including WWF, they are trying to find a balance to curb poaching and promote regulated fishing and its revenue. As part of conservation efforts, WWF-Mongolia works on scientific researches, education campaigns, and public awareness. Take a look at the Mongolian Fish guidebook to know more!
#50 parading shrimp
A long time ago, a group of indigenous people in north-eastern Thailand discovered a distinctive phenomenon called ‘parading’– the synchronous mass migration of freshwater shrimps on land. Found in rivers and streams of Asia - Viet Nam, Yunnan (China), Laos, Thailand, and Peninsular Malaysia - Macrobrachium dienbienphuense is one of the species known to parade annually. During the rainy season, these adventurous shrimps leave the water collectively at night and walk upstream on land before returning to the river. But why would they leave the water? Recent research conducted by Watcharapong Hongjamrassilp in Nam Yuen district (Ubon Ratchathani province, Thailand), tested the hypothesis that parading was associated with spawning and breeding – and it is not. Evidence shows that the shrimps might leave the water to escape strong currents. Most of the parading shrimp were juveniles – larger adults can face a stronger current, being less likely to parade – and not ready to reproduce. They walked from 5 to 20 meters - depending on river velocity and riverbank structure - and some even stayed out of water for 10 minutes or more. To take in oxygen while on land, shrimp stayed within the rivers splash zone (20–40 cm from the river’s edge), and their exoskeleton seemed to trap water around their gills (similar to a reversed dive helmet). This mass migration is such a fascinating scene that it has been promoted as an ecotourism event in Thailand since 1999, drawing more than 100.000 visitors annually. Even though they are listed as Least Concern on the IUCN Red List of Threatened Species, recent evidence suggests that they are decreasing in number and body size.
#49 water boatman
You can likely find the tiny water boatman, Micronecta scholtzi, in the bottom of ponds and streams, rowing with their paddle-shaped legs. M. scholtzi is a species of lesser water boatman found in Europe. Micronecta’ means small swimmer, but the only thing small about them is their size. Despite being only 2 millimetres long, this aquatic insect can produce the loudest sound of any animal relative to its body size. Bigger animals generally create the loudest sounds – mechanically speaking, a small sound source cannot generate a high-level sound output. In terms of sheer decibels, M. scholtzi loses to whales and elephants. Yet, this little creature can still produce a sound loud enough to be heard from a riverbank several meters away, propagating it across the water-air interface. Only males can sing – they generate an extremely loud courtship call to attract females, often in a synchronized chorus. And how do they sing? Scientists believe they rub their penis against ridges on their abdomen and that layers of air around their body amplify the sound. Water boatman specimens trap air reserves through microscopic hairs as they dive to help them breathe. Such a sound-producing genitalia mechanism is relatively rare within the animal kingdom.
#47 GREEN ANACONDA
To say that the Green anaconda, Eunectes murinus, is fascinating is an understatement. They belong to one of the most remarkable Neotropical freshwater snakes groups - the Anacondas - known for their constricting abilities and as one of the world’s longest snakes. Green anacondas stand out as the heaviest snake – it can weigh up to about 250kg! They also have a “heavy” diet, including Earth’s biggest rodent (Capybaras - see below #39) and the occasional crocodilian (Caimans). This species is widely distributed through the swamps, marshes, and slow-moving streams of South America. Green anacondas’ eyes and nasal openings are on the top of their head, which allows them to “hide” as they stay completely submerged in the water while waiting to ambush their prey. With a lethal squeeze that halts breathing and blood flow, prey is killed and then swallowed. Green anacondas also form “breeding balls” – slow-motion wrestling matches of a dozen suitors for one receptive female, where they simultaneously coil around her until one of them gets lucky. The impregnated female retains the eggs, and her offspring emerges from the eggs before leaving her body. She then gives birth to two to three dozen live young, which are already about two feet long and almost ready to swim.
The iconic jaguar, Panthera onca, is the largest cat in the Americas. From Mexico to Argentina, jaguars typically inhabit regions with dense forest cover and water bodies, living near lakes, rivers, and wetlands. They are more strongly associated with water than any other Panthera cats. This majestic species is a confident swimmer known to cross large rivers, and it preys on aquatic species like turtles and even caimans. Thanks to their robust canines and a large head, jaguars can take down prey three to four times their own weight and bite through a crocodile skull or turtle shell – having the most powerful bite than any other big cats. Therein lies its name – ‘jaguar’ comes from ‘yaguar’, an indigenous word that means 'he who kills with one leap'. Sadly, they have been nearly eliminated from half of their historic range, with regional extinctions in El Salvador and Uruguay. Their preference for freshwater habitats - even within drier areas, they are only found around the main watercourses – quickly brings them into human-wildlife conflict, as they share the same resource as the expanding high-intensity agriculture and mining. Illegal wildlife trade, and habitat loss and fragmentation are other threats leading to the decreasing population of jaguars, listed as Near Threatened by the IUCN Red List. Their stronghold is in Brazil – in the Amazon region and the world’s largest tropical wetland, the Pantanal. However, the recent fires in both biomes magnify the threats to these populations - especially in the Pantanal, where a park known to hold the biggest concentration of jaguars globally has had 85% of its territory burned.
#46 Elephant fish
Campylomormyrus curvirostris has a very long trunk-like snout and occurs exclusively in water bodies within the Congo River basin. This strange-looking fish is a species within the family of freshwater weakly-electric fishes, the Mormyrids. This - mostly - nocturnal family is known to use their electric sense to communicate, actively find objects and food, and discriminate between fish from other species and their own. A specialized electric organ in the tail base generates a mild pulse-like Electric Organ Discharge (EOD). The electric pulse helps them to create a picture of their surroundings, in a similar way bats and dolphins use echolocation. C. curvirostris belongs to a particular group within their Mormyrids family – the Campylomormyrus –, which scientists say to have EOD play a key role in pair formation and mate recognition. The species in this group show remarkable differences in terms of EOD shape and duration, which enables them to perceive differences in the EOD generated by their peers.
#45 Giant Otter
As the name conveys, the Giant otter, Pteronura brasiliensis, is the largest otter species in the world - reaching lengths up to 170cm-180 cm. They live in large and slow-moving rivers, streams, lakes, and swamps throughout South America’s lowland rainforests and wetlands. Giant otters are very social, living in large family groups that do everything together – sleeping, hunting, and playing. Generally, a monogamous pair that mate for life leads the group formed by their offspring. As they are diurnal, noisy, and hang out in groups, they can be easy to see - making them highly susceptible to persecution. Giant otters were nearly hunted to extinction for the pelt trade between the 1940s and mid-1970s and lost from much of their southern and easterly range, including Uruguay, Argentina, and several states of Brazil. Besides poaching, they currently face threats such as habitat loss, pollution, and diseases introduced by domesticated dogs. The Giant otter is listed as Endangered by the IUCN Red List, with a decreasing population trend and a discontinuous and fragmented range due to local extinctions. Important subpopulations can be found in the Pantanal region and in the Amazon, including in Peru, where the otter biologist, Jessica Groendikj, worked on the individual identification of the Giant otter. One of this species' distinctive features is the pale markings on its neck - as unique as your fingerprints - making them identifiable from birth.
#44 Vagrant darter
The Vagrant darter, Sympetrum vulgatum, is a dragonfly species found in all kinds of standing, largely unshaded waters. Larvae of almost all 5952 species of dragonflies and damselflies depend on freshwater habitats, spending most of their lives in this stage (generally one or two years) in the water. The nymphs live on the bottom of still and slow-ﬂowing waters. To fully grow into an adult, the larvae catches and eats live prey at every opportunity. Both larvae and adults are predators, playing a signiﬁcant role in the cycle of materials both in aquatic and terrestrial ecosystems. The Vagrant darter is a rare migratory species with a wide distribution – you can find this species eastwards to China and Japan, in Central and eastern Europe, and is likely common in large parts of its Asian range.
#41 Sulawesi Cardinal shrimp
The colourful Sulawesi cardinal shrimp, Caridina dennerli, is only known from Lake Matano in Indonesia (part of the Malili Lakes system - Sulawesi). However, the vivid colours of this freshwater shrimp are fading from the lake - they have not been recorded since 2013 and are listed as Critically Endangered by the IUCN Red List of Threatened Species. Reinforcing this trend, surveys conducted in 2017 and 2018 recorded not a single specimen in the lake, not even from sites where they were abundant before. Hence, this species is now considered Possibly Extinct in the Wild, being among the 1 in 3 freshwater species threatened with extinction. The Sulawesi shrimp is currently under the threat of nickel mining and hydropower installations on the outlet of Danau Matano, which impacts outflow and natural water level fluctuations. The rapidly expanding human population, erosion around the lake, capture for the pet trade, and direct predation of invasive species aggravate the problem. IUCN’s conservation efforts on the Lake Malili system aim to raise awareness and improve conservation and sustainable use by assessing freshwater biodiversity status and distribution. Shoal - an organisation dedicated to the conservation of freshwater species - is working on a Conservation Action Plan in Wallace’s dreamponds to step up the conservation sufficiently to a scale that will allow the endemic species to survive and recover. You can also learn more about the impacts on freshwater species and habitats with WWF’s Living Planet report 2020 and what you can do to help.
#43 Sockeye salmon
For the Sockeye salmon, Oncorhynchus nerka – size doesn’t count. Even though it is among the smaller of the seven Pacific salmon species, the bright-orange Sockeye salmon migrates thousands of kilometres during their lifetime from rivers to the ocean and back again. They hatch in gravel nests in rivers or lakes of Russia, Canada, and the United States and stay in freshwater for one to three years before migrating to the ocean. They remain in the sea for one to three years until maturity - when they are ready to go back to their natal freshwater habitat, where they spawn and die. Scientists think that salmon navigate back to their natal rivers by following the geomagnetic drift, along with visual, olfactory, and environmental cues from currents, salinity, water temperature, and freshwater inputs from rivers. As with other salmonids, the Sockeye needs clean, cool, and highly oxygenated water for their sensitive eggs to thrive. Therefore, a healthy population of salmon acts as a good indicator of river health. Recently, the Living Planet Index for Migratory Freshwater Fish highlighted the 76% collapse in freshwater migratory fish populations around the world since 1970 due to overexploitation, river dams blocking their migration routes, and habitat degradation. Sockeye salmon is listed as stable by the IUCN Red List of Threatened Species; however, some subpopulations are declining, and there are cases of regional extinction. WWF conservation efforts focus on protecting salmonids and their habitats through initiatives such as Free-Flowing Rivers and programmes in the Arctic, where we work with local communities.
The (Duck-billed) Platypus, Ornithorhynchus anatinus, is one of the most peculiar animals on the planet. This species uniqueness starts with the order of mammals to which it belongs - monotremes, mammals that lay shell-covered eggs but nurse their young. With its duck-like bill, webbed feet, a broad flat beaver-like tail, and an otter type of body and waterproof fur, this distinct mammal is adapted to and dependent on freshwater ecosystems. Hunting underwater, these bottom feeders have skin folds to cover their eyes and ears to prevent water from entering, and the nostrils close with a watertight seal. They find their invertebrate prey by detecting electrical signals through sensitive receptors on their bill, storing the catch in their cheek pouches until they reach the surface for consumption. They are also among the few venomous mammals – males have sharp stingers on the heels of their rear feet, using them most likely to settle territorial disputes. But don’t worry - although excruciating, the toxic blow is not fatal to humans, but known to kill mice, dogs, and other platypuses. Nowadays, you can only find the Platypus in the streams, lakes, and lagoons of eastern Australia and Tasmania – it was extinguished from much of its range due to hunting, habitat degradation, river fragmentation from dams, and entrapment or entanglement in ﬁshing gear.
#40 Oriental darter
The Oriental darter, Anhinga melanogaster, is a waterbird known for its ability to swim to catch fish and other underwater prey. Found in Southern Asia, this beautiful bird lives in shallow inland wetlands, including lakes, rivers, swamps, and reservoirs. With their webbed toes, darters swim with their bodies submerged, while their long and sinuous neck remains visible above water. This behaviour display gives darters a snake-like appearance – accounting for their colloquial name “snakebird”. When foraging, they move slowly or hang motionless in the water, spearing fish with their dagger-like bill. Adapted to diving in shallow waters, darters are renowned for their extremely low buoyancy. Compared to other closely-related water birds like cormorants, they have uncommonly wettable plumage, thin and less spongy skin, denser bones, and smaller air sacs. Like other water birds, they are important bioindicators for the ecological conditions and health of wetland ecosystems. The Oriental darter is listed as Near Threatened by the IUCN Red List of Threatened Species, being regionally extinct in Thailand. Their populations are decreasing due to pollution, drainage, hunting, and the collection of eggs and nestlings. As they warrant conservation attention, Oriental darters are harboured by WWF’s Orissa Semi-Evergreen Rain Forests ecoregion.
#38 Nile Crocodile
The Nile crocodile, Crocodylus niloticus, is an aquatic predator that can reach up to 6 meters. Found in eastern, central, and southern Africa, this reptile giant inhabits a wide diversity of water bodies (rivers, lakes, swamps, and coastal estuaries), including the iconic Mara river basin. WWF’s recent report on Mara’s freshwater biodiversity identified the Nile crocodile as one of the four freshwater reptiles in the basin shared by Kenya and Tanzania. This species plays a key predatory role in the perennial river, which is the only water source for migrating wildlife in a drought year. They mostly feed on fish but can attack zebras, small hippos, porcupines, birds, and even other crocodiles. This impressive animal presents a caring nature as a parent – females ferociously guard and defend their nests until the eggs hatch, often helping hatching babies emerge with their teeth and carrying them inside their mouths to the water. This species also presents other sophisticated behaviour like complex communication and coordinated group hunting, being considered highly intelligent. If you ever thought that a crocodile has a dinosaur-like feature, you were not far off - crocodilians are more closely related to dinosaurs and birds than to most reptiles. Between the 1940s and 1960s, the Nile crocodiles populations were depleted throughout much of their range due to hunting. Thanks to the protection afforded by national legislation and international trade conventions (CITES), populations have recovered in many regions.
The capybara, Hydrochoerus hydrochaeris, is the largest rodent on Earth. This mammal depends on freshwater ecosystems, occurring only in a habitat close to water like marshes, estuaries, rivers, and streams. They are adapted to a semi-aquatic life, using water for mating, to escape from predators, and to eat aquatic plants. Due to their dry skin (their sweat glands are not well developed), they stay in the water or under shade – especially in the afternoon - to regulate their body temperature. Capybaras have toes partially webbed to paddle around and eyes, ears, and nostrils on the top of their head to keep an eye on their surroundings. They are fundamentally social animals - female capybaras raise the offspring in groups and cooperate in their nursing. Broadly distributed, you can find capybaras mostly in South America - Colombia, Venezuela, Ecuador, Peru, the Guianas, all of Brazil, eastern Bolivia, Paraguay, Uruguay, and north-western and eastern Argentina. Their primary threat is hunting for meat and leather, with some local populations extirpated. The most recent threat is the gargantuan fires in the Pantanal – the world’s largest wetland and one of the habitats with the highest density of capybara (learn more about WWF’s actions against the fires here).
#37 blue-spotted Mudskipper
The blue-spotted mudskipper, Boleophthalmus pectinirostris, is one peculiar fish. It belongs to a group known for its incredible ability to live in and out of water - the amphibious “gobies” fish. Thanks to adaptations like their strong pectoral fins, they can move on land in a way called “crutching” – similar to a human walking with crutches. They can also jump and climb up streams and waterfalls through their partly or entirely fused pelvic fins that function as a strong sucker. To breathe out of the water, mudskippers use their skin and chambers in their modified gills to trap air. Found in Northwest Pacific, the blue-spotted mudskipper lives in freshwater, brackish, and demersal habitats, including mudflats in Mai Po Nature Reserve’s wetlands in Hong Kong. During high tides, they stay in a burrow in the mud. They “crutch” around and browse the mudflats at low tide, being so numerous that the mud can almost seem alive. Males commonly display dramatic territorial and mating behaviours, like facing each other head-on and raising their dorsal fins as threats or to attract females. Sadly, illegal fishing and habitat degradation threaten their populations (learn more with this great read and check them out in this video).
#35 Piraputanga fish
The Piraputanga fish, Brycon hilarii, is renowned for its leaping ability. Endemic to the Upper Paraguay river basin, they play an important (long-distance) role in seed dispersal in the Pantanal region as they perform long pre-spawning migrations along all river drainages. The Piraputanga uses its scissor-like teeth to feed on fruits that fall in the water. They can also leap up to one (1) meter above the water to snatch fruits (and insects) from the riparian vegetation! This remarkable behaviour is a common attraction for tourists, who bait fruit above the water to see the beautiful Piraputanga leap. The Piraputanga also captivates its audience with its colour – when the light reflects on the water, the scales of Piraputangas showcase a flaring contrast of their yellow body, orange-colored fins, and red tail. They are also an essential source of income for local communities through recreational diving and fish watching, as well as artisanal or sport fishing. Sadly, the destruction of riparian forests and construction of dams negatively impacts aquatic ecosystems, threatening seasonal migratory movements of frugivorous fishes. Overfishing or other anthropogenic disturbances (like pollution) might also lead to the local extinction of fish–plant interaction, which may negatively affect the riparian forests in this region and have far-reaching implications on ecosystem services livelihoods.
#34 raft spider
Meet the European spider of the year: the raft spider, Dolomedes fimbriatus, one of the largest native spiders in the region. Found mostly in moorland and wetlands, they inhabit water margins of ditches, ponds, and slow-flowing streams, showing remarkable adaptations to this habitat. This free-living hunter spider moves skilfully on the water surface, overpowering its prey without using a web. They sit on emergent water plants or the water surface in a hunting position, waiting for unaware (aquatic) insects, tadpoles, and small fish. Thanks to its thick coat of body hairs, the raft spider can lay its whole body on the water, relying on surface tension to remain above the water. But when in danger, they can dive underwater and come out dry – an air bubble forms around their body, which bursts after they go back to the water surface. Raft spider females constantly carry their spherical egg-sacs (with up to 1000 eggs!) in their mouthparts called chelicerae (pair of appendages in front of the mouth). When the eggs are close to hatching, the female hangs the eggs’ cocoon in vegetation near the water’s edge, guarded and enclosed by silk threads. Unfortunately, the Euro-spider of the year is becoming rarer and more vulnerable, due to the destruction of its habitat – building work on river banks and removing reed beds and water lilies - and climate change.
#36 pink Amazon river dolphin
“Once the sun goes down, the boto morphs into a handsome young man dressed in white to seduce young women of local villages, leaving them impregnated before the sun comes up to return to the river once again as dolphins.”
That’s not the only myth surrounding the pink Amazon river dolphin, Inia geoffrensis. Also known as “boto cor-de-rosa” or boto, you can find this mystical animal throughout the Amazon and Orinoco river basins in South America (strictly speaking, also in the Araguaia basin). Unlike other river dolphins, the boto has a flexible neck that moves its head left and right to maneuver through the flooded forests for food and shelter. With their long snout, they feed on fish and other aquatic organisms like turtles and crabs. Locals believe that botos possess magical powers. If you swim alone in the river, you could be whisked away by the boto to “Encante”, a magical underwater city. For many tribes, including WWF, the boto is sacred. Listed as an Endangered species by the IUCN Red List, the magical boto can’t escape threats such as dams, mercury poisoning due to gold mining, and being killed in fishing nets or to be used as fish bait. Through initiatives such as River Dolphin Rivers and South American River Dolphin (SARDI), WWF works with local communities, governments, and other NGOs to develop regional and innovative approaches to protecting this species and their habitats. Since they are indicators of environmental river health, the pink river dolphin was chosen as the Ambassador of the Amazon rivers! With such seductive powers, that was an easy call.
#32 Sacred lotus
To shine some light on these trying times, we bring you the Sacred lotus, Nelumbo nucifera. This perennial aquatic plant has been revered in many cultures for thousands of years, mostly as a symbol of purity. Its name derives from its significance in the religions of Buddhism and Hinduism: a plant that rises from a humble origin, rooting itself in the muck below and ascending high above the water untainted. The leaves can sit directly or above the water, and the distinguished lotus flower blooms gloriously above the leaves. The Sacred lotus’s uniqueness is in all parts of the plant - the roots, stems, leaves, and seeds have all been used as a food source and in traditional medicines, especially in Southeast Asia. Also known as the Asian lotus, this species has also intrigued the scientific community for presenting remarkable features such as leaf super-hydrophobicity (i.e., water repellence) - known as the “Lotus-Effect” -, and seed longevity. Their leaves have a special waxy coating that sheds water and dirt, suggesting that the Lotus-Effect may play an important role in protecting plants against pathogens and contaminations. Lotus fruits were found buried underground over 1300 years in China could still be germinated, being seed longevity another fantastic feature of this sacred aquatic plant.
#33 Harvest mouse
The super cute Harvest mouse, Micromys minutus, loves a wetland! Especially in Europe, where they are quite common in wetlands. Harvest mice make their nests in the reeds or along rivers and canal edges, and feed on seeds, green vegetation and insects. This species of rodent is an extremely active climber and has an acute hearing - they react sharply in response to rustling sounds up to 7m away, freezing or dropping into cover. But they can’t always react fast enough – their numbers have been noted to decline in many parts of Europe, particularly local populations, due to loss and degradation of wetland habitats. In Sussex, England, the Ouse and Adur Rivers Trust created the project Helping Hands for Harvest Mice Citizen Science, where as part of a wider river restoration project, local communities have helped researchers monitor harvest mouse populations.
#30 Mekong Giant Catfish
Able to reach a length of up to 3m and over 300kg, the Mekong giant catfish, Pangasianodon gigas, is one of the world’s largest fish! Native and endemic to the Mekong River, this species can live to be 60 years old. These migratory fish swim around Vietnam, Cambodia, Laos, and Thailand – most likely found in the Lower Mekong river basin. Sadly, they are one of the most endangered fish in southeast Asia. Listed as Critically Endangered by the IUCN Red List of Threatened Species, this species faces overharvesting for local and commercial fisheries, habitat loss and pollution, intentional hybridization for aquaculture, and bag-net fishery of Cambodia. In the last 50 years, the total number of fish declined by 90%. This river giant is a highly-valued food resource, not because it is a delicacy but because it has a god-like status - some believe it brings good luck forever once eaten, bestowing the gifts of wisdom and long life. Intentional fishing is currently banned in most areas, but this species is still harvested incidentally as by-catch. As the Mekong giant catfish most probably migrates long distances, dams’ construction is also a threat. Dams likely prevent them from reaching their spawning site and may cause extinction - there is only one known spawning site in Thailand, and the blockage of this waterway by two dams might be their demise.
#28 Ywangan crocodile newt
New species are often discovered in the biodiversity hotspot region of the Greater Mekong - over 2,216 new species have been found since 1997 (that’s two species per week on average! Check this report for more). Recently, researchers discovered a new species of newt. With a coloration almost solid black, the Ywangan crocodile newt, Tylototriton ngarsuensis, differs from its bright orange cousins, besides having a shorter head, larger size, and breeding later in the year than other closely related species. Found in Ngar Su Village, in Myanmar, this amphibian is so common that the villagers have long known about it. One of the researchers, Lee Grismer, said that “even in populated areas, new species can be found and in doing so underscores the need for field work so we can more accurately catalogue the biodiversity of this planet.” Especially when these species face threats such as habitat destruction, harvest for the illegal pet trade, and medicinal trade. Besides Lee Grismer, this new species was discovered by his colleague from La Sierra University, Marta S. Grismer, Perry L. Wood Jr. (University of Kansas), Evan S.H. Quah (Universiti Sains Malaysia), Robert E. Espinoza (California State University) Matthew L. Murdoch (Villanova University, USA), and Aung Lin (Fauna and Flora International, Myanmar).
#31 Great diving beetle
The Great diving beetle, Dytiscus marginalis, is an aquatic insect generally found in still waters with dense vegetation. These ferocious carnivores can grow up to 44mm feeding on arthropods, tadpoles, newt larvae, and juvenile ﬁshes. With dorsoventrally compressed and oval bodies perfectly adapted for swimming, diving beetles propel themselves through their legs’ synchronous strokes covered with swimming hairs. As diving beetles mostly breathe atmospheric air, they carry a bubble of air under their wings when swimming under the water surface – quite like scuba divers! Likewise, they also have to come to the surface occasionally to replenish the oxygen in the bubble. When resting underwater in well-oxygenated streams, this air bubble can function as a physical gill capable of absorbing dissolved oxygen from the surrounding water.
#29 American beaver
The cuddly-looking American beaver, Castor canadensis, is one of the two species of beavers in the world. The North American native has darker fur and a shorter snout than its Eurasian “cousin”, but both are stars when it comes to their constructions - beavers are second only to humans in their ability to change and manipulate their environment. Living in areas of persistent water like lakes, ponds, and streams, beavers build dams and dome-shaped homes with branches and mud to protect themselves and their offspring against predators. The dams block streams and turn land into large ponds, facilitating the floating of food and building material to their homes - often strategically placed in the middle with only underwater entrances. Beavers’ leathery tails storage energy (fat) and their characteristic large front tree-razing teeth never stop growing, which they control by constantly gnawing on wood. Due to their diet of leaves and bark, to some people, beavers’ butts smell like vanilla! To waterproof and scent mark themselves, they use a special grooming paw on their hind foot to distribute throughout their fur castoreum oil - a chemical compound often the combination of castor and anal gland secretions, plus urine (watch this video to learn more about them).
#27 Mary River turtle
This week we bring you the mesmerizing Mary river turtle, Elusor macrurus. This captivating species can be found in flowing, well-oxygenated sections of streams in a single river of Australia – its namesake, the Mary river. One of their unique features is having an extremely long tail, which can be as long as 70% of the shell length. But what makes this funny-looking freshwater turtle even more special is its ability to breathe through its bum! The Mary river turtles have a cloacal ventilator – gill-like structures on their cloacas, which allows them to breathe oxygen underwater up to three days. Unfortunately, their unique looks are the reason they are listed as Endangered by the IUCN Red List of Threatened Species. During the 1960s and 70s, thousands of Mary river turtle eggs were harvested for the pet trade, leading to their dramatic population declines. It was their looks, on the other hand, that helped to prevent the construction of a dam in 2009 in the Mary River, which would have put them at even higher risk. The struggle, however, is far from over as the Mary river turtle continues to be threatened by feral animals, cattle grazing and water quality.
#26 Fisherman bat
This week we present a flying mammal that can also fish – the Fisherman bat, Noctilio leporinus. Also known as the Greater Bulldog bat, this fishing bat inhabits tropical lowlands from Southern Mexico to Northern Argentina, foraging over streams, ponds, rivers, and lagoons. The Fishermen bat can swim and take ﬂight from the water, and feeds on aquatic insects, ﬁsh, frogs, and crustaceans. Many bats are associated with freshwater, but ﬁshing bats possess adaptations of their posterior limbs to capture prey. Fishing bats tend to have 1.8 to 3.9 times larger feet, and their digits – ''toes'' - are elongated, ending with hook-like claws. When fishing, these bats fly within 20 to 50 cm of the water surface, echolocating to find ripples that signal underwater prey. Once they notice the disturbance, they fly closer over the water (four to 10cm) with their back legs and feet held straight down, “scraping” the water to gaff fish with their forward-facing claws. With the fish in their claws, they rise in the air and transfer the prey to their mouth. The Fishermen bats are also safe “flyers” – when on a collision course with other fellow Fishermen, one bat "honks" at the other! They can do this by adjusting the frequency of its echolocation call.
#25 Electric eel
To celebrate World Rainforest day, we present this shocking species, Electrophorus voltai. Two new electric eel species were discovered last year in the Greater Amazonia region. One of the new species, Electrophorus voltai, can generate an electric shock up to 860 V, the strongest of any known animal. More than five times the voltage of a standard American wall socket, researchers say that this shock wouldn’t kill a healthy person, although it would definitely not be pleasant and result in a brief muscle contraction, then numbness. Electric eels generally use their electric discharge to detect other fish and paralyze prey. The researchers, however, also found that electric eels seem to coordinate their predatory activity; they surround the fish as a group, release electricity, and kill it. If you want to know more, check out the scientific paper here.
#24 Water scorpion
The Water scorpion, Nepa cinerea, might look like it, but it is not a true scorpion. With its leaf-shaped and flattened body, this intriguing species is actually a water bug – an insect adapted to freshwater ecosystems. Frequently found in the Palaearctic region – a large ecozone including Europe, Asia, northern Africa, and the north and central parts of the Arabian Peninsula – the Water scorpion swims via strong strokes, and crawls and clings to water plants. When at rest, they slyly hide upside-down amongst the vegetation, letting their breathing tube out of the water to catch atmospheric air. They track their prey furtively, approaching the fry of insect larvae with considerably slow, almost inconspicuous movements. As soon as the unaware prey is within some millimetres, the Water scorpion swiftly embraces its victim with its raptorial front legs.
The Axolotl, Ambystoma mexicanum, is a rare and intriguing species endemic to Mexico and one of the few fully aquatic salamanders in the world. They have a deep-rooted cultural significance in the region, but nowadays are found exclusively in Lake Xochimilco, near Mexico City. Their funny-looking (and charismatic) appearance is due to a unique characteristic known as neoteny – the retention of juvenile features, such as external gills, despite reaching sexual maturity. Presenting an astonishing and one-of-a-kind ability to regenerate body organs and lost limbs, Axolotls are on the spotlight of cellular regeneration research – they can even receive transplanted organs from other individuals and accept them without rejection. Sadly, this extraordinary species is listed as Critically Endangered on the IUCN Red List of Threatened Species mainly due to two factors: poor water quality and the introduction of non-native fish species, especially the Oreochromis niloticus (Tilapia) through competition and predation. Within conservation efforts, the work of the Sisters of Immaculate Health stands out – they are skilful Axolotl breeders! To save one of the world’s most endangered and most remarkable amphibians, the amazing nuns partnered with conservationists from Chester Zoo (find out more about their work here).
#21 Painted terrapin
The striking Painted terrapin, Batagur borneoensis, is a freshwater turtle native to Brunei Darussalam, Indonesia, Malaysia, and Thailand. They present plain grey skin and shell for most of the time, letting their beautiful colours only pop during the mating season from January to June. The males are the ones to go through the transformation and “paint” themselves – their carapace lightens in colour to showcase striking black markings, and their heads turn to pure white with a bright red strip between their eyes. The female terrapins nest in beaches, but instead of the new-borns (a.k.a hatchlings) heading to the open ocean like their sea-going “cousins”, they make their way towards fresh and brackish waters. After reaching their mating age, pregnant Painted terrapins return to the same beach where they once hatched to lay their own eggs - the circle of life! This predictable behaviour, however, is one of the reasons this species is listed as Critically Endangered on the IUCN Red List of Threatened Species – it makes them vulnerable to habitat destruction and poachers who steal the eggs to eat or sell. Learn more about this incredible species and WWF conservation efforts with this great read.
Endemic to Lake Malawi in East Africa, the Chambo, Oreochromis karongae, likes to swim around in loose shoals. Like other fishes of the Oreochromis genus, they present a curious form of parental care called maternal mouthbrooding. During spawning, soon after the male has fertilized the eggs, the mother puts them in her mouth until they hatch – a fascinating strategy to protect their offspring. The Chambo is also very important for local subsistence and commerce, being the most valuable food fish in Malawi. For this reason, they are threatened by overfishing. In the 1990s, the populations of the Chambo collapsed, with a 70% decline within ten years – unsurprisingly ending up listed as Critically Endangered by the IUCN Red List of Threatened Species.
The flatworm, Crenobia alpina, is not your typical freshwater star species. With two primitive eyespots giving them a charismatic look, this species can grow up to 15mm in length (take a look at them moving here). This harmless flatworm is a predator found most frequently in cold and clear mountain streams. Their preference for cold waters comes with a price in a climate-changing world – a 40-year study shows that this species (as well as other invertebrates) has vanished from Llyn Brianne and much of Wales when the temperature of the streams rose. As the professor of ecology at Cardiff University’s school of biosciences, Steve Ormerod says, “the loss of freshwater organisms is a hidden tragedy, and it’s amazing how much is left to discover”.
#19 Spoon-billed sandpiper
The Spoon-billed sandpiper, Calidris pygmaea, is a petite wading bird with a unique spatula-shaped bill. With their heads down in shallow and wet meadows, they move their bills side to side to look for food, also using it sometimes as a shovel. This migratory bird has a very specialised breeding habitat found in north-eastern Russia – lagoon spits where they can nest among crowberry plants, dwarf birch, and willow sedges with adjacent estuary or mudflats. During winter, they migrate down the Pacific coast to Southeast Asia – relying heavily on intertidal areas of the Yellow Sea along the way. Unfortunately, their stopover habitats, as well as their breeding and wintering grounds, are being degraded, resulting in the Spoon-billed sandpiper being one of the world’s most endangered birds. They are listed as Critically Endangered by the IUCN Red List of Threatened Species. As a response, the Spoon-billed sandpiper is one of the priority species of our Asian Flyways initiative, which aims to restore and protect an international network of wetlands used by this and other migratory birds populations.
#18 Freshwater jellyfish
Did you know that jellyfish also exist in freshwater systems? Native to the Yangtze River valley in China, the Freshwater jellyfish, Craspedacusta sowerbii, prefers to live in still or slow-moving water bodies such as ponds, reservoirs, quarries, and lakes. Similarly to other jellyfish, they have a complex life cycle that generally includes 5 moments: microscopic podocytes (dormant "resting bodies"), two different larvae phases, polyp phase, and the most recognizable (but least common in the environment) – the hydromedusa (right picture). As opportunistic predators, the Freshwater jellyfish feeds on small organisms that come within its reach, capturing their prey with the (in)famous stingers. But there’s no need to worry next time you take a dip in a lake - the stinging cells are so small that they usually don’t hurt vertebrates.
#17 Lesser Flamingo
This week we celebrate the exquisite and outstanding Lesser flamingo, Phoenicopterus minor. This species is “lesser” only in the sense that it is the smallest of the six species of the flamingo family. They have the biggest population of all flamingos, with two to three million individuals. They are also tolerant to extreme environments – their habitat is hostile for many animals and plants due to high temperatures, salinity, and alkalinity, but the Lesser flamingos are superbly adapted. Living around lagoons or lakes of Africa and India, they walk through shallow waters with their thin, pink legs as they feed - bending their necks downward to filter their food. It is thanks to their diet - rich in carotenoid pigments - that their feathers become remarkably pinkish. The bright pink colouration may function as a signal of parental capability, attracting mating partners – as parents take turns in brooding, one of them needs to look for food efficiently. The Lesser flamingo also shines with their spectacular courtship dance: groups of more than 1000 birds march together with a straight-up posture like soldiers, moving their heads and necks synchronously. These extraordinarily social birds also synchronize other activities such as brooding, to “crowd-protect” their offspring. A recent study even suggests that they form lifelong friendships – making it impossible not to fall for the flamboyant flamingo.
#16 The Waterwheel plant
The Waterwheel plant, Aldrovanda vesiculosa, might seem harmless with its tiny and delicate appearance while free-floating its “rootless-self” in peat-bog pools, lakes, and river deltas. Especially for an unsuspecting small aquatic invertebrate, who gets unwittingly too close to the Waterwheel and…SNAP! It is trapped in their prey-catching leaves. This remarkable and rare carnivorous aquatic plant has a snap-trap system that can be set off inadvertently by their game - the prey stimulates, mechanically, trigger hairs found in the central region of the trap leaves, prompting the two trap lobes to rapidly (as short as ten milliseconds!) move toward each other. Sadly, this unique species is listed as Endangered by the IUCN Red List of Threatened Species, known in only 50 isolated populations across the globe. The Waterwheel plant faces many threats, including eutrophication and degradation of its wetland habitat, driven by unsustainable agriculture and development.
#15 Irrawaddy river dolphin
To celebrate Dolphin Day (April 14th), we present to you the charming Irrawaddy river dolphin, Orcaella brevirostris. With a rounded head and no beak, the three subpopulations of this distinctive dolphin can be found swimming along three rivers in South and Southeast Asia - Ayeyarwady River (Myanmar), Mahakam (Indonesia) and Mekong (Cambodia). Recent estimates indicate that there are around 79 individuals left on the Ayeyarwady, indicating this is a species right on the edge. Nonetheless, less than 300 freshwater Irrawaddy dolphins still live, including in Cambodia and Indonesia. Although they are not directly exploited, these river dolphins suffer many threats, including entanglement in gill nets and illegal fishing activities such as electrofishing - which unsustainably removes their food source. Nevertheless, fishing activities can be done in harmony with river dolphins. In the Ayeyarwady river, the local fisherfolk use a traditional fishing method that portrays a unique relationship with the dolphins, called “Cooperative fishing”. The fishermen “call” the dolphins by tapping a stick repeatedly on the side of the boat. If the dolphins are up to fishing, they chase shoals of fish towards the waiting nets and signalize the location of the prey. Once the fishermen cast their nets, the dolphins snatch the escaping fish. As this extraordinary interaction can be seen only in a few places around the world, many initiatives – such as our River Dolphin Rivers - work on the conservation of both the Irrawaddy dolphin and the fishermen’s way of life.
#14 Surinam toad
The Surinam toad, Pipa pipa, is a fully aquatic amphibian known for its unusual appearance and fascinating – some might argue horrifying - parental care adaptations. You can find this species mostly in the slow-flowing waters of the Amazon Basin in South America, generally hiding under submerged leaf-litter - with their extremely flattened body and triangular-shaped head, they blend in for looking like a mottled brown leaf. This species also exhibits a unique courtship behaviour: after attracting a mate by making clicking sounds, the male toad mounts onto the back of the larger female and embraces her around the waist - if she is receptive, their mating act starts, and the pair displays some aquatic somersaults that can last for more than 12 hours. With the help of the male, the fertilized eggs are rolled up onto the back of the now upside-down female – the eggs sink into the puffy and swollen skin and are almost completely enveloped by it. The pregnant toad carries the developing offspring for three to five months until the “toadlets” are ready to punch their way out of their mother’s skin pockets, in a bizarre scene that can make many people shiver.
#13 Net-spinning caddis
The Net-spinning caddis, Hydropsyche siltalai, is a species of Caddisfly; insects that are aquatic as larvae. They spend up to a year in lakes and rivers around the world before emerging as adults - and graduated engineers. One might think that larvae can’t be up to much, but the Net-spinning caddis larvae are quite busy building their retreat - a fascinating dreamcatcher-like silk structure. The larvae produce silk threads and weave it into fine-meshed nets that filter food particles from the water column while sheltering them. Recently, scientists found that these silk structures might influence local hydraulics – they can reduce flow downstream by 95% and upstream by 17%, besides altering turbulence (for more information, check the scientific paper). Even though the impressive caddis larvae seem to be well prepared to face the world and reach adulthood, recent research showed that they are in sharp decline - vulnerable to changes in climate.
#12 Arctic char
World Water Day was on March 22nd, and to celebrate our most precious resource, we introduce you to the northernmost freshwater fish in the world: the beautiful Arctic char, Salvelinus alpinus. These circumpolar fish species inhabit cold and clean waters around the North Pole. Numerous local freshwater populations of Arctic char exist in all Arctic states, plus a smaller number of sea-run populations - where fish can grow up to 10kg in weight. The Arctic char suffers from increasing temperatures due to climate change, especially the more southern populations in the Alpine regions, which can be at risk of extinction - water temperature and quality are significant factors in the survival of their sensitive eggs. According to the first report on The State of the Arctic Freshwater Biodiversity (2019), climate warming increasingly threatens freshwater biodiversity in arctic lakes, rivers, and wetlands. The report also suggests that the Arctic char – as well as other cold-water species endemic to the Arctic – are likely to suffer regional losses, or even local extinctions as a result (find out more with this great article). Similarly, the 2019 report of the Intergovernmental Panel on Climate Change (IPCC) states that changes in the cryosphere will alter freshwater communities - range shrinkage and extinction of some species can cause regional biodiversity to decrease. WWF Finland has been involved in a conservation project to strengthen the population of Critically Endangered Lake Saimaa Arctic char. Also good news exists: exploitation of the northern Arctic char population in Finland has decreased at the same time with improved protection, leading to improved conservation status in the Red Book of Species for Finland – bending the curve in freshwater species does exist!
#11 Tasmanian Giant freshwater crayfish
In the rivers and streams of Tasmania lives the world’s largest freshwater invertebrate – the endemic Giant freshwater crayfish, Astacopsis gouldi. The IUCN Red List of Threatened Species list this species as Endangered, mainly as a result of years of past overfishing, illegal fishing, and habitat loss and degradation. Capable of reaching 6kg in weight, they have been harvested as a food source at a local and national level. The effects of fishing pressure are aggravated by their biological characteristics - this menacing-looking giant is actually very easy to catch, besides being slow-growing with low breeding potential. This species has received attention as a species of conservation concern - in the 90s, the Australian and Tasmanian governments added the Giant freshwater crayfish to their environmental legislation, and, recently, the critical habitat has been redefined.
#10 Victoria water lily
A long time ago, a young warrior called Naiá, from a Brazilian Amazonian tribe – “Tupi-guarani”– would dream about the day she would meet with Jaci, the moon. According to the legend, Jaci was a goddess who every night would kiss the most beautiful women of the tribe, and before hiding behind the mountains, she would pick her favourite to transform the woman into a star. Every night, Naiá would walk around the hills searching for Jaci. One day, after seeing the reflection of Jaci on a lake, she threw herself inside the lake and drowned. The moon compassionately decided to reward Naiá for her sacrifice, transforming her into a star of the waters – the Victoria water lily, whose white flower only opens at night and changes to pink when the sun rises.
The myth of the Victoria water lily above is a fragment of the memory of WWF's Paula Martinelli, who remembers hearing this story growing up in Brazil. The Victoria water lily, Victoria amazonica, is native to the Amazon biome and the symbol of the Amazon state of Brazil. The legend of the Victoria water lily has some truth to it – the white flowers only bloom at night, its colour changing to pink or ruby red after spending the evening exuding a strong odour to attract beetles to pollinate them. The flower closes its petals in the morning, hopefully trapping the beetles and releasing pollen on them. They open again in the following evening, releasing the beetles to transport their pollen to other flowers – they now have different colours and are scentless, being less attractive to the beetles. This fascinating adaptation avoids fertilization by its own pollen, increasing the genetic variability of the world’s largest water lily.
#9 Beluga Sturgeon
To celebrate World Wildlife Day (tomorrow on March 3rd), this week we present to you the majestic Beluga sturgeon! Even though there is still a debate on which is the largest freshwater fish in the world, the Beluga sturgeon, Huso huso, is undoubtedly the largest migrating freshwater fish – with a record of 1,571 kg and 7.2 m, this female was caught in 1827 in the Volga estuary. But this is history - nowadays, you can seldom observe a length above 2m. This species has been recorded swimming in the basins of the Caspian, Black, Azov, and Adriatic Seas. The migration of the Beluga sturgeon was predictable, and as a huge fish, they were an easy target, providing abundant food for many people. Its current native wild distribution is restricted to the Black Sea (Danube and Rioni) and the Caspian Sea (Ural). It does occur in the Azov Sea and Volga River, but as stocked fish. Due to historically severe overfishing and poaching in estuaries and rivers, the Beluga sturgeon is listed as Critically Endangered (CE) by the IUCN Red List of Threatened Species. This species is wanted for its meat and caviar - one of the most valuable products on the food market. Their caviar is considered top class caviar and is among the most expensive – you can buy 30g in London at the modest price of €420, which adds up to a price of €14.000 per kg. The beluga sturgeons’ eggs can only be legally obtained from aquaculture. Unfortunately, illegal wild caviar is still in demand on the black market by customers who consider "wild" as the "real" thing. IUCN also states that sturgeons are more critically endangered than any other group of species – 23 of all 27 known species are considered to be threatened with extinction. The mighty Beluga sturgeon can live for over 100 years, spending several years in the sea and migrating longer distances than any other sturgeon – more than 1000km. Because of their particular long life cycle, the recovery of its heavily depleted stocks will need several decades. But they can still be saved. WWF is working together with communities, civil society, companies, scientists, law enforcement authorities and governments across the world to rebuild their population. For example, our Sturgeon initiative is tackling the illegal caviar trade and enhancing the health of river systems. And, last year, WWF helped to save a Beluga in the Danube.
#8 Giant freshwater stingray
The Giant freshwater stingray, Urogymnus polylepis, is one of the largest and heaviest freshwater fishes in the world. With the ability to gain more than 600kg and 2m disc width, this freshwater giant mostly swims the large rivers of south and southeast Asia ( find out more about the beautiful Giant stingray and other giants of the Mekong river in this report). The IUCN Red List of Threatened Species lists the Giant freshwater stingray as Endangered, mainly due to fisheries and habitat degradation. The development of dams is also one of the drivers for their – and other freshwater megafauna species – population declines. Among WWF’s conservation efforts is our Resilient Asian Deltas (RAD) Initiative, whose ambition is to secure healthy and functioning river systems from source to delta through unprecedented political and financial investment in ‘building with nature’. To address the crisis facing freshwater biodiversity like the Giant freshwater stingray, WWF has just published an Emergency Recovery Plan - together with scientists from across the world - as a call to action to the world’s decision makers to value, protect and restore freshwater habitats before it’s too late.
#7 Grey Crowned crane
The Grey Crowned crane, Balearica regulorum, calls attention for its beautiful colours and a majestic golden plumage on their head unfolding like a crown. They are also known for displaying playful behaviours such as dancing. Mainly a form of socialization and pair formation, other species of cranes are also famous for their dance moves. You can find the Grey Crowned crane “performing” in the eastern and southern regions of Africa, where they are also a culturally important species – considered icons of Africa’s wetlands and savannahs, besides being the national bird of Uganda. However, it’s not all glamour for the Grey Crowned crane. Listed as Endangered by the IUCN list of threatened species, they are threatened primarily by illegal trade, disturbance, and habitat loss. The Global Wetland Outlook 2018 states that up to 87% of wetlands have been lost since 1700. The Grey Crowned crane and the other 14 living species of cranes need wetlands as stepping stone corridors – where they can find a safe harbour to sleep, rest, nesting, and rearing the young. As cranes are among the most threatened bird families in the world, WWF has joined the International Year of Crane 2020, announced by the International Crane Foundation and the Crane Working Group of Eurasia. The Amur River basin is the flyway and breeding grounds of no less than six species of cranes, and WWF will be working with partners in the region to strengthen the conservation of both wetlands and the majestic cranes.
#3 Hellbender Salamander
The Hellbender salamander, Cryptobranchus alleganiensis, a.k.a. giant salamander, is, non-surprisingly, the largest salamander in North America – and the third-largest in the world. But these amphibian giants are fascinating not only for their size: they have lungs, but they mostly breathe through their wrinkly skin; they can swim, but usually walk underwater through their sturdy limbs. With tiny eyes on the top of their heads and light-sensitive cells all over their bodies, especially on their tails, they can keep their (giant) selves completely hidden from large fish under rocks and use their keen sense of smell to hunt crayfish. Besides playing this important role in their ecosystem, they are also bioindicators of stream quality, as they have a low tolerance for poor water quality. It is not a good sign for the North American rivers that their populations are considered Near Threatened by the International Union for Nature Conservation (IUCN), mainly due to the worsening condition of their freshwater habitats. Find out more about this species in this cool video by David Herasmtschuk.
#6 Rainbow mussel
The Rainbow mussel, Villosa iris, is a fascinating freshwater species not only for its beautiful inside shell, which is iridescent – they are also the master of disguise! “Hidden” in the North American rivers and streams, this tiny mussel uses mimicry to increase its odds of success: the mussel lures fishes by looking and moving like a crayfish, which is, in reality, a few flaps of fleshy skin coming out of its shell. Once the fish is close enough to take a bite of the “crayfish”, the Rainbow mussel releases a cloud of tens of thousands of parasitic spawn! Aiming for a safe place to transition into juvenile mussels, the mussel larvae latch to the fish’s gills, fins, and skin. Their new “home” (and “ride”) also provide for their food – they feed on the minuscule amounts of nutrients from their host. Most of the time, however, the fooled host-fish is not harmed by this interaction.
#4 Yangtze Finless porpoise
The Yangtze Finless porpoise, Neophocaena asiaeorientalis asiaeorientalis, as the name suggests, lives in the Yangtze River and is the world’s only freshwater porpoise – and one of only five surviving species of freshwater cetacean. Unfortunately, there are only an estimated 1,012 finless porpoises left in China’s greatest river and they are listed as Critically Endangered on the IUCN red list of threatened species due to a host of threats, including water pollution, overfishing, boat traffic, sand mining, and river fragmentation. Many finless porpoises have also been killed after becoming accidentally entangled in gill nets – something which contributed to the extinction of the Yangtze freshwater dolphin, the Baiji (Lipotes vexillifer). But there is still hope for the Yangtze finless porpoise. Led by the Chinese government, conservation efforts – involving WWF, partners and local communities – have helped to drastically slow the annual decline in the finless porpoise population, including relocating animals to safer habitats away from the river’s mainstem to create new breeding populations. Huge amounts of work still need to be done to secure the survival of the species and WWF will continue to be at the forefront through its global River Dolphin Rivers initiative. This initiative is working on the development of smart river pingers in an effort to prevent future entanglement in gillnets. For many years, the finless porpoise had little to smile about but thanks to the combined efforts of the government, communities and conservationists, there is now a chance that the species can turn the corner and that its population will finally start to increase.
#5 Golden Mahseer
The Golden Mahseer, Tor putitora, is one of the world’s most iconic freshwater fish – highly prized by anglers, it is viewed as a God fish by local communities in some parts of South Asia, such as India and Bhutan. But its numbers are declining across South and South East Asia due to a range of threats from dam blocking its migratory routes to pollution and unsustainable fishing. It is now classified as Endangered on the IUCN Red List of threatened species. Local communities in India have revered fish species as symbols of divine power, offering them protection and building temple sanctuaries along the river banks, the first established nearly 1200 years ago. The Golden Mahseer benefits from this protection in several stretches of the river Ganges associated with these temples, where fishing is not allowed, and local communities, pilgrims, and temple authorities help to monitor and protect the mahseer population. The Mahseer also has cultural, religious and economic significance in Bhutan, where it is known as the Tiger of the River (you can find out more in this great documentary on the “Tiger of the River” produced by WWF Bhutan). In 2015, as a response to the pressures on Bhutan’s river systems, the Fisheries Conservation Foundation, WWF Bhutan, and the Ministry of Agriculture and Forests started a partnership to assess the migration pattern of the God fish using radio telemetry technology. This year, the 2nd International Mahseer Conference is being held in Thailand from 11th to 15th February, where researchers and conservationists - including WWF - will share knowledge, collaborate and promote the conservation of the species.
#2 Matamata turtle
The matamata turtle, Chelus fimbriata, is one of the world’s largest freshwater turtles – and undeniably one of the weirdest too. Found in the Amazon and Orinoco basins, their unmistakable appearance is the combination of a leaf-shaped head, a long pointy snout, a rough tuberculate flat shell, and an elongated, thick neck with protuberances. The bizarre look is the result of a unique adaptation for feeding and blending in - they are incredibly specialized feeders that wait for dinner to come to them. When unknowing fish approach them to see if the protuberances on their neck are edible, they quickly stretch their neck out and open their mouth to create a vacuum that swallows their prey whole.
#1 European eel
For the first week we are highlighting the European eel, Anguilla anguilla. There can be few species more mysterious than the European eel, Anguilla Anguilla. A species that breeds just once in its lifetime and must travel thousands of kilometres to do so. European eels, like other Anguillid eels exhibit a number of life stages: they start their lives in the ocean as leptocephalus (larvae) which float back to estuaries where they turn into glass eels, and then elvers before travelling upstream into our rivers where they turn into yellow eels. The final stage of an European eel’s life is as a silver eel; silver eels are able to migrate thousands of kilometres to the Sargasso sea to spawn. No one has witnessed their spawning and so the spawning location remains a hypothesis. European eels are a Critically Endangered species, threatened by dams and infrastructure, habitat destruction and illegal trafficking. Find out more about this enigmatic and mysterious freshwater species in this great article.
If you’d like to find out about other Anguillid species, check out this blog from Kathy Hughes, our very own Freshwater Habitats and Species ACAI lead. Kathy like’s eels so much she takes holidays especially to swim with them.