Swamps are characterized by poorly drained mineral soils and by plant life dominated by trees. Potholes are depressional wetlands found primarily in the upper Midwest. They were formed by glaciers in prehistoric times. Bogs are characterized by deposits of spongy peat and extensive growth of evergreen trees and shrubs. A bog floor is usually covered by a thick carpet of moss.
Fens are peat-forming wetlands that support diverse plant and animal communities.
They are often covered by grasses, sedges, reeds, and wildflowers. They are actually a type of open freshwater marsh that receives nutrients from upland sources, not from precipitation. Playa lakes are the flat-floored bottom of an undrained desert basin that at times becomes a shallow lake. Wetlands play an important role in local ecosystems, supporting great biodiversity. The combination of shallow water, high levels of nutrients, and rich plant life is ideal for the development of organisms that form the base of the food web and feed many species of fish, amphibians, shellfish, and insects.