Wetlands are ecosystems consisting of land covered either permanently or seasonally by water. They can include marshes, ponds, edges of lakes and seas, river deltas, and low-lying areas that are prone to flooding.

Wetlands make up an estimated 4 to 6 percent of the Earth’s land area and are found in all ecosystems.

Some wetlands, including swamps and marshes, are among the planet’s most productive ecosystems. As they provide habitats for both terrestrial and aquatic species, they often have higher biodiversity than do other ecosystems. They also serve as important carbon and nutrient sinks.

Wetlands also provide considerable benefits to humans. Most notably, they support fisheries, agriculture and timber production, provide water supply, create opportunities for recreation and tourism, and can absorb large amounts of water during flooding. Even in cities, where they were once drained to make way for buildings and urban infrastructure, wetlands are making a comeback.

There are five major natural wetland types:

• marine (coastal wetlands including coastal lagoons, rocky shores, and coral reefs)
• estuarine (deltas, tidal marshes, and mangrove swamps)
• lacustrine (wetlands associated with lakes)
• riverine (wetlands along rivers and streams)
• palustrine (marshes, swamps and bogs).

Read the rest of our ‘fast facts’ series on ecosystems below.

• Forests
• Agriculture
• Mountains
• Peatlands
• Oceans
• Drylands and rangelands