Freshwater swamp forest in Bangladesh
Peat bogs are freshwater wetlands that develop in areas with standing water and low soil fertility.
Marshes develop along the edges of rivers and lakes.

A wetland is a distinct ecosystem that is inundated by water, either permanently or seasonally, where oxygen-free processes prevail.[1] The primary factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation of aquatic plants,[2][3] adapted to the unique hydric soil. Wetlands play a number of functions, including water purification, water storage, processing of carbon and other nutrients, stabilization of shorelines, and support of plants and animals.[4] Wetlands are also considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life. Whether any individual wetland performs these functions, and the degree to which it performs them, depends on characteristics of that wetland and the lands and waters near it.[5] Methods for rapidly assessing these functions, wetland ecological health, and general wetland condition have been developed in many regions and have contributed to wetland conservation partly by raising public awareness of the functions and the ecosystem services some wetlands provide.[5][6]

Wetlands occur naturally on every continent.[7] The main wetland types are swamp, marsh, bog, and fen; sub-types include mangrove forest, carr, pocosin, floodplains,[1] mire, vernal pool, sink, and many others. Many peatlands are wetlands. The water in wetlands is either freshwater, brackish, or saltwater.[3]Wetlands can be tidal (inundated by tides) or non-tidal.[8] The largest wetlands include the Amazon River basin, the West Siberian Plain,[9] the Pantanal in South America,[10] and the Sundarbans in the Ganges-Brahmaputra delta.[11]

The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth.[12]

Constructed wetlands are used to treat municipal and industrial wastewater as well as stormwater runoff. They may also play a role in water-sensitive urban design.


A patch of land that develops pools of water after a rain storm would not necessarily be considered a "wetland", even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.[13][14]

A more concise definition is a community composed of hydric soil and hydrophytes.[1]

Wetlands have also been described as ecotones, providing a transition between dry land and water bodies.[15] Mitsch and Gosselink write that wetlands exist "...at the interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both."[16]

In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions.

Technical definitions

Sunrise at Viru Bog, Estonia

A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic and aerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding."[17] There are four main kinds of wetlands – marsh, swamp, bog and fen (bogs and fens being types of mires). Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types.[1] The largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia.[9]

Ramsar Convention definition

Under the Ramsar international wetland conservation treaty, wetlands are defined as follows:[18]

  • Article 1.1: "...wetlands are areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water the depth of which at low tide does not exceed six metres."
  • Article 2.1: "[Wetlands] may incorporate riparian and coastal zones adjacent to the wetlands, and islands or bodies of marine water deeper than six metres at low tide lying within the wetlands."

Regional definitions

Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes. In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas".[19] This definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's.

In the United States Code, the term wetland is defined "as land that (A) has a predominance of hydric soils, (B) is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation typically adapted for life in saturated soil conditions and (C) under normal circumstances supports a prevalence of such vegetation." Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions (not unusually dry or unusually wet), and in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, and those conditions will persist through the wet portion of the growing season.[20]

Other Languages
Afrikaans: Vleiland
العربية: منطقة رطبة
বাংলা: জলাভূমি
Bân-lâm-gú: Tâm-tē
беларуская (тарашкевіца)‎: Водна-балотныя ўгодзьдзі
български: Влажна зона
català: Zona humida
čeština: Mokřad
chiShona: Matoro
Deutsch: Feuchtgebiet
eesti: Märgala
Ελληνικά: Υγροβιότοπος
español: Humedal
Esperanto: Malsekejo
euskara: Hezegune
فارسی: تالاب
français: Zone humide
galego: Zona húmida
한국어: 습지
हिन्दी: आर्द्रभूमि
Bahasa Indonesia: Lahan basah
íslenska: Votlendi
italiano: Zona umida
Kreyòl ayisyen: Tè makay
latviešu: Mitrājs
lietuvių: Šlapynė
македонски: Моклиште
Bahasa Melayu: Tanah lembap
Nederlands: Drasland
नेपाली: सिमसार
日本語: 湿地
norsk: Våtmark
norsk nynorsk: Våtmark
ਪੰਜਾਬੀ: ਜਲਗਾਹ
پنجابی: جلگاہ
polski: Mokradło
português: Zona úmida
română: Zonă umedă
Scots: Wetland
සිංහල: තෙත්බිම්
Simple English: Wetland
slovenčina: Mokraď (ekológia)
slovenščina: Mokrišče
suomi: Kosteikko
svenska: Våtmark
Türkçe: Sulak alan
اردو: آبستان
Tiếng Việt: Đất ngập nước
粵語: 濕地
Zazaki: Erdo awın
žemaitėška: Šlapīmė
中文: 湿地