Marsh vegetation controls soil and water runoff from upland areas, helping to protect rivers, bays and adjacent lands from flooding. Marshes also help control sedimentation, eutrophication, and pollution of waterways. Within these broad categories, more specific types can be distinguished, such as low and high marshes in the tidal salt marsh. Each marsh type is associated with characteristic plants which are adapted to prevailing conditions including frequency of flooding by tides and levels of salt in the water. Marsh Distribution Salt marshes are found along the coast behind barrier islands and beaches, and the lower portion of the Chesapeake Bay.
Brackish marshes occur along the edges of estuaries and tidal rivers and streams.
Freshwater marshes occur on the tidal rivers and streams above the influence of salt water, and may also be found inland around ponds, lakes, rivers, and streams. In Virginia, most marsh habitat is found in the coastal plain. A lack of trees and tall shrubs means that marsh-nesting birds must build their nests close to or on the ground, on a clump of emergent vegetation, or in the limbs of a low shrub. Nesting season for all these birds falls within a period from late April through August. The Least Bittern, the smallest member of the heron family, nests in brackish and freshwater tidal marshes.