The Everglades is a natural region of tropical wetlands in the southern portion of the U.S. state of Florida, comprising the southern half of a large drainage basin within the neotropic ecozone. 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 (97 km) wide and over 100 miles (160 km) 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. The Seminole Tribe gave the large body of water the name Okeechobee meaning "River of Grass" to describe the sawgrass marshes, part of a complex system of interdependent ecosystems that include cypress swamps, the estuarine mangrove forests of the Ten Thousand Islands, tropical hardwood hammocks, pine rockland, and the marine environment of Florida Bay. Throughout the 20th century, the Everglades suffered significant loss of habitat and environmental degradation.
A 2007 survey by geographers Ary J. Lamme and Raymond K. Oldakowski found that the "Glades" has emerged as a distinct vernacular region of Florida. It comprises the interior areas and southernmost Gulf Coast of South Florida, largely corresponding to the Everglades itself. It is one of the most sparsely populated areas of the state.
Fluctuating sea levels compressed numerous layers of calcium carbonate, sand, and shells. The resulting permeable limestone formations that developed between 25 million and 70 million years ago created the Floridan Aquifer, which serves as the main source of fresh water for the northern portion of Florida. However, this aquifer lies beneath thousands of feet of impermeable sedimentary rock from Lake Okeechobee to the southern tip of the peninsula.
The metropolitan areas of Miami, Fort Lauderdale, and West Palm Beach are located on a rise in elevation along the eastern coast of Florida, called the Eastern Coastal Ridge, that was formed as waves compressed ooids into a single formation. Along the western border of the Big Cypress Swamp is the Immokolee Ridge (or Immokolee Rise), a slight rise of compressed sand that divides the runoff between the Caloosahatchee River and The Big Cypress. This slight rise in elevation on both sides of the Everglades creates a basin, and forces water that overflows Lake Okeechobee to creep toward the southwest. Under both the Miami Limestone formation and the Fort Thompson limestone lies the Biscayne Aquifer, a surface aquifer that serves as the Miami metropolitan area's fresh water source. Rainfall and stored water in the Everglades replenish the Biscayne Aquifer directly.
Water is the dominant force in the Everglades, shaping the land, vegetation, and animal life in South Florida. Starting at the last glacial maximum, 21,000 years ago, continental ice sheets retreated and sea levels rose. This submerged portions of the Florida peninsula and caused the water table to rise. Fresh water saturated the limestone that underlies the Everglades, eroding some of it away, and created springs and sinkholes. The abundance of fresh water allowed new vegetation to take root, and formed convective thunderstorms over the land through evaporation.
Alligators have created a niche in wet prairies. With their claws and snouts they dig at low spots and create ponds free of vegetation that remain submerged throughout the dry season. Alligator holes are integral to the survival of aquatic invertebrates, turtles, fish, small mammals, and birds during extended drought periods. The alligators then feed upon some of the animals that come to the hole.
Although The Big Cypress is the largest growth of cypress swamps in South Florida, cypress swamps can be found near the Atlantic Coastal Ridge and between Lake Okeechobee and the Eastern flatwoods, as well as in sawgrass marshes. Cypresses are deciduous conifers that are uniquely adapted to thrive in flooded conditions, with buttressed trunks and root projections that protrude out of the water, called "knees". Bald cypress trees grow in formations with the tallest and thickest trunks in the center, rooted in the deepest peat. As the peat thins out, cypresses grow smaller and thinner, giving the small forest the appearance of a dome from the outside. They also grow in strands, slightly elevated on a ridge of limestone bordered on either side by sloughs. Other hardwood trees can be found in cypress domes, such as red maple, swamp bay, and pop ash. If cypresses are removed, the hardwoods take over, and the ecosystem is recategorized as a mixed swamp forest.
From the Glades peoples, two major nations emerged in the area: the Calusa and the Tequesta. The Calusa was the largest and most powerful nation in South Florida. It controlled fifty villages located on Florida's west coast, around Lake Okeechobee, and on the Florida Keys. Most Calusa villages were located at the mouths of rivers or on key islands. The Calusa were hunter-gatherers who lived on small game, fish, turtles, alligators, shellfish, and various plants. Most of their tools were made of bone or teeth, although sharpened reeds were also effective for hunting or war. Calusa weapons consisted of bows and arrows, atlatls, and spears. Canoes were used for transportation, and South Florida tribes often canoed through the Everglades, but rarely lived in them. Canoe trips to Cuba were also common.
By 1913, the Seminole in the Everglades numbered no more than 325. They made a living by hunting and trading with white settlers, and raised domesticated animals. The Seminole made their villages in hardwood hammocks or pinelands, had diets of hominy and coontie roots, fish, turtles, venison, and small game. Their villages were not large, due to the limited size of the hammocks. Between the end of the last Seminole War and 1930, the people lived in relative isolation from the majority culture.
The Everglades Forever Act, introduced by Governor Lawton Chiles in 1994, was an attempt to legislate the lowering of phosphorus in Everglades waterways. The act put the South Florida Water Management District (SFWMD) and the Florida Department of Environmental Protection (DEP) in charge of testing and enforcing low phosphorus levels: 10 parts per billion (ppb) (down from 500 ppb in the 1980s). The SFWMD built Stormwater Treatment Areas (STAs) near sugarcane fields where water leaving the EAA flows into ponds lined with lime rock and layers of peat and calcareous periphyton. Testing has shown this method to be more effective than previously anticipated, bringing levels from 80 ppb to 10 ppb.