Swamps are generally characterized by very slow-moving waters, often rich in tannins from decaying vegetation. 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, although they may be surrounded by mountains.
The most famous swamps in the United States are the Okefenokee Swamp (home to the cartoon characters of Pogo, by Walt Kelly) 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, was created by the New Madrid earthquake of 1812. Both the Great Dismal and Reelfoot are centered around large lakes.
Swamps are characterized by rich biodiversity and specialized organisms. For instance, southeastern U.S. swamps, such as those mentioned above, feature trees such as the Bald cypress and Water tupelo, which are adapted to growing in standing water, and animals such as the American alligator.