In physical geography, a wetland is an environment that combines the properties of land and water. Wetlands are a distinct kind of ecosystem.

The combination of wet and dry areas means that many more different kinds of plants, animals and insects may live in a wetland than compared to other types of habitat. Because of this great biodiversity, several important wetlands are among the Global 200 ecoregions that the World Wide Fund for Nature listed for conservation to try to get people to protect them. As well, Ramsar Convention is adopted in 1971 for protection of wetland.

Wetland types 
 A bog or muskeg is acidic peat land (peat bog).
 A moor was originally the same as a bog but has come to be associated with this soil type on hill-tops.
 A moss is a raised bog in Scotland
 A fen is a freshwater peat land with chemically basic (which roughly means alkaline) ground water. This means that it contains a moderate or high proportion of hydroxyl ions (pH value greater than 7).
 A carr is a fen which has developed enough to support trees. It is a European term, mainly applied in the north of the UK.
 A fresh-water marsh's main feature is its openness, with only low-growing or "emergent" plants. It may feature grasses, rushes, reeds, typhas, sedges, and other herbaceous plants (possibly with low-growing woody plants) in a context of shallow water. It is an open form of fen. The Fens in eastern England were just such a wetland.
 A coastal (salt)-marsh typically has very salty water, either directly from the ocean or a mixture of salt water and fresh water. Salt-marshes may be associated with estuaries and along waterways between coastal barrier islands and the inner coast. The plants in this kind of marsh can range from reeds in mildly brackish (salty) water to especially hardy salt-grasses (salicornia) on otherwise bare marine mud. Many plants in salt-marshes have evolved to live in such salty conditions with special adaptations. Salt-marshes may be converted to human use as pasture (salting) or for salt production (saltern).
 A swamp is wetland with more open water surface and deeper water than a marsh. In North America, 'swamp' is used for wetlands dominated by trees and woody bushes rather than grasses and low herbs. This distinction does not necessarily apply in other areas, for instance in Africa where swamps may be dominated by papyrus instead of trees. A swamp may also be described by the dominant plants growing in it. For example: A mangrove swamp or mangal is a salt or brackish water environment dominated by mangrove trees. A paperbark wetland is a fresh or brackish water environment dominated by the Melaleuca tree.
 A dambo is a shallow, grass-covered depression of central and southern Africa. It is waterlogged in the rainy season, and usually forms the headwaters of a stream or river. It is marshy at the edges and at the headwater, but maybe swampy in the centre and downstream.
 A bayou or slough are southern United States terms for a swamp with a creek running through it. In an Indian mangrove swamp, it would be called a creek.
 A peat swamp forest is a low-level tropical or subtropical forest wetland. It produces peat, and is sometimes called a blackwater swamp.
 A constructed wetland is man-made to make a piece of land hold more water than it otherwise would naturally. This allows the land to stay wet enough to grow wetland plants and oftentimes hold water as well. Uses include absorbing flash floods (by holding the extra water from the flood), cleaning sewage (which is done by the plants as the dirty water passes over their roots), enhancing wildlife habitat (for example creating new homes for rare birds or other animals) or for some other human reason.

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