They may be defined as areas in which the water table is near, at, or above the surface of the soil for all or part of the year. The water in a wetland reaches this level for enough time to promote the development of damp soils and to restrict growth to plants adapted to a wet environment. Wetlands are found on every continent except Antarctica, in climates ranging from tropical to tundra. There are three general types of wetlands. However, because the character of a wetland area depends heavily upon its water source, there may be great variation within these categories.
Marshes contain nonwoody emergent plants.
There may be different zones within one marsh which vary with respect to the relationship between the height of the soil and the height of the water. Different plant species may inhabit these different zones. Marshes may have either salt water or fresh water and soil may vary greatly in mineral and organic quality. Swamps contain large amounts of trees or shrubs. They may vary greatly in salinity and nutrient content of soil.