The ecosystem it forms is not presently found anywhere else on earth. The system begins near Orlando with the Kissimmee River, which discharges into the vast but shallow Lake Okeechobee. Water leaving the lake in the wet season forms a slow-moving river 60 miles wide and over 100 miles long, flowing southward across a limestone shelf to Florida Bay at the southern end of the state. The Everglades experience a wide range of weather patterns, from frequent flooding in the wet season to drought in the dry season. Throughout the 20th century, the Everglades suffered significant loss of habitat and environmental degradation.

       Five geologic formations form the surface of the southern portion of Florida: the Tamiami Formation, Caloosahatchee Formation, Anastasia Formation, Miami Limestone, and the Fort Thompson Formation. The Tamiami Formation is a compression of highly permeable light-colored fossiliferous sands and pockets of quartz, 150 feet thick. It is named for the Tamiami Trail that follows the upper bedrock of the Big Cypress Swamp, and underlies the southern portion of the Everglades. Between the Tamiami Formation and Lake Okeechobee is the Caloosahatchee Formation, named for the river over it. Much less permeable, this formation is highly calcitic and is composed of sandy shell marl, clay, and sand. Water underneath the Caloosahatchee Formation is typically very mineralized. Both the Tamiami and Caloosahatchee Formations developed during the Pliocene Epoch.

       Surrounding the southern part of Lake Okeechobee is the Fort Thompson Formation: made of dense, hard limestone, shells, and sand. Rain water is less likely to erode the limestone to form solution holes—smaller versions of sinkholes that do not intersect with the water table. In this formation the beds are generally impermeable. Underneath the metropolitan areas of Palm Beach County is the Anastasia Formation: composed of shelly limestone, coquina, and sand representing a former mangrove or salt marsh. The Anastasia Formation is much more permeable and filled with pocks and solution holes. The Fort Thompson and Anastasia Formations, and Miami Limestone, were formed during the Sangamonian interglacial period.

       (from Wikipedia)