In geography, a marsh, or morass, is a type of wetland which is subject to frequent or continuous flood. Typically the water is shallow and features grasses, rushes, reeds, typhas, sedges, and other herbaceous plants. Woody plants will be low-growing shrubs. A marsh is different from a swamp, which has a greater proportion of open water surface and may be deeper than a marsh. In North America, the term "swamp" is used for wetland dominated by trees rather than grasses and low herbs.

The water of a marsh can be fresh (freshwater marsh), brackish (brackish marsh), or saline (salt marsh).

Coastal marshes may be associated with estuaries, and are also along waterways between coastal barrier islands and the inner coast. The estuarine marsh, or tidal marsh, is often based on soils consisting of sandy bottoms or bay muds. An example is the Tantramar Marsh of eastern Canada.

Marshes are critically important wildlife habitat, often serving as breeding grounds for a wide variety of animal life, particularly including ducks and geese.

Constructed wetlands featuring surface-flow design are usually in the form of a marsh.

Decomposition of plant materials below water often produces marsh gas, which may begin to burn by self-ignition making mysterious lights known locally as Will o' the wisps, Jack-o'-lanterns, or sprites.

See also

• Aquatic plant
• Bayou
• Biodiversity Action Plan
• Bog
• Fen
• Slough

Reference line notes

• Marshes of the Lowcountry (South Carolina) -- Beaufort County Library
• General Information of Ibera Marshes (in English and Spanish)