Freshwater Biodiversity | WWF
© Andre Dib/WWF

Freshwater Species of the week

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.

© Michel Roggo


#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.

© La Ponte


#42 Platypus

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. 

© Peter Maguire


#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.

© WWF-Malaysia / Mazidi Abd Ghani


#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

© Jaime Rojo Lopez


#39 capybara

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).

© Martin Harvey / WWF


#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.  

© Magnus Lundgren / Wild Wonders of China / WWF


#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).

© / Mark Carwardine / WWF


#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.  


© Patrik Oening / WWF-Brazil


#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.

© Anne Richardson


#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.

© Izzy Standbridge


#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. 

© Barthlott, Univ. Bonn


#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.

© Jan Hamrsky


#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. 

© Zeb Hogan / WWF


#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.

© Gary Graham

#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).

© Lee Grismer


#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). 

© Chris van Wyk


#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.

© Denis Faure


#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.

© Leandro Souza


#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.

© Jan Hamrsky


#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. 

© Chris Martin Bahr / WWF


#23 Axolotl

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).

© Barry Warrington


#22 Flatworm

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”.

© Muhammad Zaid Nasir / WWF Malaysia


#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.

© Pr. George F. Turner, IUCN


#20 Chambo

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. 

© Jan Hamrsky


#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.

© Peter Chadwick / WWF


#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.

© Barthlott, Univ. Bonn


#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. 

© / Roland Seitre / WWF


#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.  


© Myron Tay


#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.

© Arthur D. Chapman


#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.

© Johannes Sipponen / WWF


#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!

© Jan Hamrsky


#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.

© Andre Dib / WWF Brasil


#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. 

© Ryan Francis


#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. 

© WWF/Jiri Bohdal


#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.

© Martin Harvey / WWF


#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.

© Tim Lane


#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. 

© WWF India


#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.

© Zeb Hogan WWF


#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.

© Justin Jin WWF US


#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.

© Visual Unlimited WWF


#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.

© Meridith Kohut WWF-US


#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.

© Tim Watt


#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.


If you want more information on our Freshwater Species of the Week, or even suggest an increadible species, please contact Paula Martinelli ( 

© Tim Watt