What makes a place a wetland?

A wetland is a place where water covers the soil, or lies at or near its surface, for all or part of the year. Swamps, marshes and bogs are all wetlands.

The water shapes everything else. Because the ground stays soaked, wetlands develop their own kind of soil, known as hydric soil, and they support plants called hydrophytes, which are adapted to grow in waterlogged ground.

Wetlands fall into two broad groups. Coastal, or tidal, wetlands are found where rivers meet the sea and salt water mixes with fresh: salt marshes full of hardy grasses and, in the tropics, mangrove swamps. Inland wetlands lie on the flat land beside rivers, in hollows in the ground, at the edges of lakes and ponds, and wherever groundwater keeps the soil wet. They include marshes, wet meadows, and swamps of shrubs or trees.

Not every wetland is wet all the time. Many inland wetlands are seasonal and dry out for part of the year, especially in dry regions, and some pools fill with water only now and then. Yet even these provide vital homes for wildlife. Wetlands are found from the frozen tundra to the tropics, on every continent except Antarctica, and they support animals of both land and water in one place.