Substantial loss of prairie potholes has increased flooding and contaminated agricultural land and drinking water. Freshwater marshes are often found at the edge of lakes and rivers. The vegetation in freshwater marshes, dominated by herbaceous plants, is frequently quite diverse. These wetland regions are valuable for filtering water and providing habitat for wildlife, such as birds, reptiles and amphibians. Swamps are dominated by woody vegetation, such as bald cypress, cedars, maples, willows and oaks.
Swamps are often wet part of the year and dry the rest of the year.
Many large swamps can be found along the Mississippi River. If managed correctly, these wetlands can be a good source of wood products. In river systems, swamps help control flooding by slowing the water downstream and leveling flood peaks. Bogs are freshwater peatlands that occur mostly at northern latitudes in the coterminous United States, in parts of Alaska and in Canada. They have a low pH, are usually dominated by sphagnum mosses and certain coniferous trees, and support a number of rare plant species.