What is a wetland?
Lakes and ponds
The shorelines and shallow inlets of lakes support a great diversity of plant and animal life. The muddy lake bottom is home to a host of creatures - flatworms, segmented worms, molluscs, crustaceans and insect larvae. The tangled roots of reeds and rushes provide shelter for breeding fish, frogs and newts. Water birds and a variety of mammals nest and feed in the wetland vegetation near the shore.
Specially adapted creatures
Even a small pond is home to a myriad of species. Shallow ponds and marshes might dry up for part of the year: the animals that live here need to survive in a dormant state during dry periods, or move to another pond. The African lungfish, which can grow to 2m long, buries itself in the drying mud and covers itself with a slimy cocoon so that its skin stays moist.
It can stay there for many months, breathing in air and waiting for the rains to come. Some other varieties of fish can even travel across land! In India, climbing perch travel from pond to pond since their gills absorb oxygen from the air.
Creatures that live in running water have found different ways of adapting to the strong currents. Leeches, for instance, move along the bottom of a river in a series of loops, attaching their front and rear suckers alternately to river bed.
Fish are usually strong swimmers, like the rainbow trout. Other fish cling or creep over the surface of stones. Some kinds of river fish, such as the salmon family, spend much of their lives in the sea but migrate up rivers to breed.
Birds of the wetlands
Wetlands are great places to see a wide variety of bird life. Birds that feed and breed in freshwater wetlands include ducks and geese, wading birds like sandpipers and plovers, gulls and terns, herons, cranes, fish eagles, and a huge number of smaller birds like kingfishers, weavers, warblers and finches.
How they feed
Wetland birds have adapted to life in or near water in many ways. Some ducks dabble in the mud for worms and crustacea with their heads under water, others dive deep to feed on algae growing on the lake bed.
Waders have long bills for probing the mud for small worms and molluscs. Herons stand motionless by the water's edge and stab a passing fish with their dagger-like beak. The African fish eagle dives from its perch and catches fish with its sharp talons.
The waterbuck is a shaggy antelope with oily fur that feeds around wetlands in Africa. Other African antelopes that live in wetlands include the sitatunga and the water chevrotain: these two antelopes are often seen almost fully submerged in the water.
Within the smallest puddle and water-filled tree hollow you will find plants and animals. There are even animals that have adapted to life in underground cave lakes where no light penetrates.
Since vision is not of much use to them, cave-dwelling fish like the Mexican cave characin and amphibians like the Texas blind salamander are either partially or totally blind.
In the past, most people regarded wetlands as useless and disease-ridden ‘wastelands’. Huge areas of marsh in every continent have been drained for agriculture, or filled in for building sites.
River banks have been straightened out and lined with concrete. Now we are beginning to realise just how valuable wetlands are, not just as areas of great biodiversity, but because they perform all kinds of useful functions like flood control and water purification.
WWF and other conservation organisations are fighting to save wetlands all over the world. Many countries are now members of the Ramsar Convention, an important international agreement to save wetlands.