A river is a natural channel of water that flows downhill. Near its source, the small river, often called a stream or a brook, flows quickly. Streams eventually join together to form a larger, slower river that flows into a lake or the sea. Both rivers and wetlands, lands that are flooded either permanently or for part of the year, are extremely important habitats for many animals.

Rivers are home to many plants and animals, both above and below the water. A fast-flowing stream is too rough, but in gentler, deeper water plants can take root in the muddy river bed. They provide food, shelter and nesting sites for many animals. Worms and snails living in the mud are food for fish, which, in turn, are eaten by otters and diving birds such as kingfishers. Mayflies and other insects living near the water’s surface are preyed upon by other insects such as dragonflies. They are also food for birds, fish and frogs.

Wetlands are found on the edge of lakes, near to the seashore or where rivers flood the land. Many plants and animals thrive in the waterlogged conditions. The Everglades of Florida, USA, is an area of slow-flowing water. The swamps are a haven for many animals, including wading birds and alligators. The waters rise and fall according to the seasons.

​​​​​​​Other important wetlands are the Okavango Delta in Southern Africa and the Pantanal in central South America. Both are flooded for part of the year, attracting many animals.