Corkscrew Swamp is a National Audubon Society sanctuary made unique by its bald cypress, the swamp itself, and wood storks. During the dry months of winter and early spring, wood storks come to Corkscrew Swamp in greater numbers than anywhere else in the United States to mate, build nests, and raise their young, before spending the rest of the year scattered across the southeastern United States. Corkscrew Swamp contains the largest stand of virgin bald cypress in the world, with some trees 500 to 600 years old; this stand was once only part of the vast old-growth forest system found throughout the Big Cypress Swamp. The swamp is part of a freshwater swamp system covering 315 square miles of southwest Florida, fed solely by rain falling across the watershed, and its water level rises and falls with the seasons so that in late spring it can be completely dry. Early settlers named Corkscrew Swamp after the twisting, turning path of the coastal river they traveled up in search of fresh water, and that river is known today as the Imperial River. Within Corkscrew Swamp Sanctuary are distinctive habitats including Pine Flatwoods, Pond Cypress, and Wet Prairie.