A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or forest swamps and "transitional" or shrub swamps. The water of a swamp may be fresh water, brackish water or seawater.
In North America, swamps are usually regarded as including a large amount of woody vegetation, but elsewhere this may not necessarily apply, such as in African swamps dominated by papyrus. By contrast, a marsh in North America is a wetland without woody vegetation, or elsewhere, a wetland without woody vegetation which is shallower and has less open water surface than a swamp. A mire (or quagmire) is a low-lying wetland of deep, soft soil or mud that sinks underfoot with large algae covering the water's surface.
A common feature of swamps is water stagnation.
Swamps are characterized by very slow-moving waters. They are usually associated with adjacent rivers or lakes. In some cases, rivers become swamps for a distance. Swamps are features of areas with very low topographic relief.
Swamps were historically often drained to provide additional land for agriculture, and to reduce the threat of diseases born by swamp insects and similar animals. Swamps were generally seen as useless and even dangerous. This practice of swamp draining is nowadays seen as a destruction of a very valuable ecological habitat type of which large tracts have already disappeared in many countries.
Atchafalaya Swamp is the largest swamp in the United States. Other famous swamps in the United States are the Everglades, Okefenokee Swamp, Barley Barber Swamp and the Great Dismal Swamp. The Okefenokee is located in extreme southeastern Georgia and extends slightly into northeastern Florida. The Great Dismal Swamp lies in extreme southeastern Virginia and extreme northeastern North Carolina. Both are National Wildlife Refuges. Another swamp area, Reelfoot Lake of extreme western Tennessee and Kentucky, was created by the New Madrid earthquake of 1812. Caddo Lake, the Great Dismal and Reelfoot are swamps that are centered at large lakes. Swamps are often called bayous in the southeastern United States, especially in the Gulf Coast region.
Swamps and other wetlands have traditionally held a very low property value compared to fields, prairies, or woodlands. They have a reputation as being unproductive land that can't be easily utilized for human activities, other than perhaps hunting and trapping. Farmers for example typically drained swamps next to their fields so as to gain more land usable for planting crops.
Societies now generally understand that swamps are critically important in the processes of providing fresh water and oxygen to all life, and are often breeding grounds for a wide variety of life. Government environmental agencies (such as the Department of Natural Resources in the United States) are taking steps to protect and preserve swamps and other wetlands.
However, the generally messy nature of swamps, with their diffuse boundaries and lack of enclosure, prevents humans from being able to collect and capitalize on their precious natural resources. Generally swamps are assessed as having low land value even while they are being protected from damage.