Freshwater swamps form around lakes and streams. Rain and seasonal flooding cause water levels to fluctuate. In the wet soil, water-tolerant vegetation grows and helps maintain a moist, swampy condition.
In many freshwater swamps in the southeastern United States, cypress and tupelo trees grow. Spanish moss may hang from the branches, and tiny plants called duckweed may cover the waters surface. Shrubs and bushes may grow beneath the trees. Sometimes poking as much as 4 meters (13 feet) above the water are angular knobs called cypress knees. They are outgrowths of the trees' root systems.
Alligators, frogs, and many other animals live in these swamps. These animals are adapted to fluctuating water levels. The shadowy tree root system and cypress knobs provide a rich, sheltered habitat for nesting birds, as well as fish, amphibians and reptiles.
The freshwater swamps between the Tigris and Euphrates Rivers in the Middle East are so rich in biodiversity that the area is called the "Fertile Crescent." The abundant wildlife, agricultural opportunities, and ability for communication and trade fostered human technological development. The Fertile Crescent is recognized as the birthplace of civilization and the site of the first cities. The earliest recorded written language and the first recorded use of the wheel occurred around these swamps.
The Everglades, in Florida, is one of the largest swamp complexes in the United States. Called the "River of Grass," this freshwater swamp is actually a wide, slow-moving river flowing from the Kissimmee River near Orlando to the Straits of Florida. The Everglades is 97 kilometers (60 miles) wide and 160 kilometers (100 miles) long. A rich collection of wildlife, from alligators to panthers, calls this freshwater swamp home.