swamp fever: see leptospirosis.

swamp, shallow body of water in a low-lying, poorly drained depression, usually containing abundant plant growth dominated by trees, such as cypress, and high shrubs. Swamps develop in moist climates, generally in such places as low-lying coastal plains, floodplains of rivers, and old lake basins or in areas where normal drainage has been disrupted by glacial deposits. In the United States, swamps cover approximately 100,000 sq mi (260,000 sq km), most of them occurring as small swamps in northeastern states that were covered with glaciers in the past. The most extensive swamps are found along the Atlantic and Gulf coastal plains, notable examples being the Everglades of S Florida, Dismal Swamp of Virginia, and Okefenokee Swamp of Georgia and N Florida. Because the bottom of a swamp is at or below the water table, swamps serve to channel runoff into the groundwater supply, thus helping to stabilize the water table. During periods of very heavy rains, a swamp can act as a natural flood control device, as excess runoff can be temporarily stored in its basin. Swamp vegetation varies with climate. Grasses, rushes, and sphagnum moss predominate in temperate climates; cypress and mangrove predominate in more tropical regions. Lush vegetation provides great protection for nesting waterfowl and fish as well as a hospitable habitat for many types of small mammal such as beaver and otter. Swamps that are drained make excellent agricultural land because of the high organic content of the bottom sediments. In addition, rising land values and demand have encouraged the drainage of many swamplands, such as coastal Florida, for home development. However, a problem associated with recently drained swamps is oxidation of the thick peat deposits forming the soil, which can result in subsidence of the land and such problems as cracked walls, broken underground pipes, and buckled roadways. The increased use of drained swampland for urban construction, with its associated acres of blacktop paving and storm sewers, results in greater runoff and increases the probability of flooding and pollution in these regions. Swamp drainage also destroys the nesting areas of many wildlife species. Thus, environmentalists have urged, with increasing success, the slowing down of swamp drainage. There are a variety of local terms for swamps, including bog, marsh, fen, and moor. However, bog usually refers to a swampy depression with a thick mat of living and dead organic matter floating on the water surface and a low level of oxygen in the water below. Marsh implies a large area of wet land where the dominant vegetation consists of low-lying grasses, rushes, and sedges.

Okefenokee Swamp, c.600 sq mi (1,550 sq km), c.40 mi (60 km) long and averaging 20 mi (32 km) in width, SE Ga., extending into N Fla. It is a saucer-shaped depression with low ridges and small islands rising above the water and vegetation cover. It abounds in varied wildlife, and is drained by the Suwanee and St. Marys rivers. In Georgia the swamp makes up most of the Okefenokee National Wildlife Refuge (est. 1937).

Dismal Swamp, SE Va. and NE N.C. With dense forests and tangled undergrowth, it is a favorite site for sportsmen and naturalists. It once may have covered nearly 2,200 sq mi (5,700 sq km) but has been reduced by drainage to less than 600 sq mi (1,550 sq km). The swamp bottom is composed of organic material deposited by fallen trees and other vegetation. Its forests still contain valuable timber, despite the lumbering and fires that have plagued the area. Dismal Swamp was surveyed in 1763 by George Washington, who was a member of a company organized to drain it. A canal 22 mi (36 km) long, which is part of the Intracoastal Waterway, was completed in 1828 and connects Chesapeake Bay with Albemarle Sound. Lake Drummond, c.3 mi (4.8 km) in diameter, in the center of the swamp, is its highest elevation. The swamp is the scene of Harriet Beecher Stowe's novel Dred.

or marsh gas

Organic compound, chemical formula CH₄, colourless, odourless gas that occurs in natural gas (called firedamp in coal mines) and from bacterial decomposition of vegetation in the absence of oxygen (including in the rumens of cattle and other ruminants and in the gut of termites). The simplest member of the paraffin hydrocarbons, methane burns readily, forming carbon dioxide and water if supplied with enough oxygen for complete combustion or carbon monoxide if the oxygen is insufficient. Mixtures of 5–14percnt methane in air are explosive and have caused many mine disasters. The chief source of methane is natural gas, but it can also be produced from coal. Abundant, cheap, and clean, methane is used widely as a fuel in homes, commercial establishments, and factories; as a safety measure, it is mixed with trace amounts of an odorant to allow its detection. It is also a raw material for many industrial materials, including fertilizers, explosives, chloroform, carbon tetrachloride, and carbon black, and is the principal source of methanol.

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Either of two large swamp trees (Taxodium distichum and T. ascendens; family Taxodiaceae) of the southern U.S. that are related to the sequoias. The hard red wood of cypress is often used for roofing shingles. The so-called deciduous cypress family (see deciduous tree) comprises 10 genera with 15 species of ornamental and timber evergreen trees, native to eastern Asia, Tasmania, and North America. The leaves on a single tree may be scalelike, needlelike, or a mixture of both. Both male and female cones are borne on the same tree. The Tasmanian cedar (Athrotaxis), Japanese cedar (Cryptomeria japonica), China fir (Cunninghamia lanceolata), umbrella pine (Sciadopitys verticillata), big tree, redwood, dawn redwood, and bald cypress are economically important timber trees in this family.

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Freshwater wetland ecosystem characterized by poorly drained mineral soils and plant life dominated by trees. Swamps have a sufficient water supply to keep the ground waterlogged, and the water has a high-enough mineral content to stimulate decay of organisms and to prevent the accumulation of organic materials. They are found throughout the world. Seealso marsh.

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Swamp and wildlife refuge, southeastern Georgia and northeastern Florida, U.S. It has an area of more than 600 sq mi (1,550 sq km). Located about 50 mi (80 km) inland from the Atlantic coast, it is bounded by the low, sandy Trail Ridge, which prevents direct drainage into the Atlantic. It has diverse and abundant wildlife. Exotic flowers, such as rare orchids, abound. In 1937 a large area of the swamp, almost all in Georgia, was made the Okefenokee National Wildlife Refuge.

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or Great Dismal Swamp

Wetland region, southeastern Virginia and northeastern North Carolina, U.S. Despite much lumbering and widespread destruction by fire, the area is still heavily wooded. About 30 mi (48 km) long and 10 mi (16 km) wide, it is home to many rare birds and numerous poisonous snakes. Noted for its fishing and hunting, it is traversed by the Dismal Swamp Canal, part of the Atlantic Intracoastal Waterway.

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