Everglades Geography: Where It Is, What It Sits On, How It Drains

The surviving Everglades are a set of managed units south of Lake Okeechobee: five Water Conservation Areas, the Holey Land and Rotenberger Wildlife Management Areas, and Everglades National Park, which includes Florida Bay (South Florida Water Management District, Everglades).

The South Florida Water Management District (SFWMD) names the Water Conservation Areas as WCA 1, WCA 2A, WCA 2B, WCA 3A and WCA 3B, and notes that WCA 1 is also the Arthur R. Marshall Loxahatchee National Wildlife Refuge (SFWMD Everglades). Florida law uses its own list. Section 373.4592 of the Florida Statutes, the Everglades improvement and management law, defines the Everglades Protection Area as Water Conservation Areas 1, 2A, 2B, 3A and 3B, the Loxahatchee refuge and Everglades National Park (section 373.4592, Florida Statutes). The two Wildlife Management Areas on the SFWMD list are not named in that statutory definition.

Everglades National Park itself lies along the southernmost Florida peninsula in Miami-Dade, Monroe and Collier counties and takes in most of Florida Bay between the peninsula and the Keys (NPS Geodiversity Atlas, Everglades National Park). The National Park Service gives its size as about 610,660 hectares, or 1,508,976 acres, and dates it to authorization on May 30, 1934, and establishment on December 6, 1947 (NPS Geodiversity Atlas).

SFWMD says the Everglades once covered almost 11,000 square miles of South Florida and are today half the size they were a century ago (SFWMD Everglades).

The same SFWMD page also describes the historical Everglades as roughly 40 miles wide by 100 miles long, running from the south shore of Lake Okeechobee to the mangrove estuaries of Florida Bay, and sizes the Everglades and Florida Bay system at approximately 2 million acres, a system that contains the largest subtropical wetland in the United States (SFWMD Everglades). The page gives the 11,000 square mile figure and the 40 by 100 mile outline side by side without reconciling them.

A wider frame comes from a 2003 U.S. Geological Survey publication, which puts the South Florida ecosystem at approximately 28,000 square kilometers supporting more than 5 million people, with the natural systems of the Kissimmee, Okeechobee and Everglades watershed competing for water with cities, farms and tourism (USGS, Measuring and mapping the topography of the Florida Everglades). A UF/IFAS Extension publication, citing a 1993 study, tallies the losses: about 2,500 square kilometers of the Everglades lost to the East Coast Protective Levee, about 11,650 square kilometers of watershed degraded by the levee around Lake Okeechobee, and just over 15,000 square kilometers of marsh and watershed lost with the Water Conservation Areas and the Everglades Agricultural Area (UF/IFAS EDIS UW199).

The Everglades rest on limestone, a calcium carbonate rock that rarely reaches the surface because flat wetlands and grasses cover it (USGS, Geology and Hydrology of Everglades National Park).

The National Park Service says the Everglades formed 5,000 years ago atop a bedrock of porous limestone (NPS Everglades, Nature). Its Geodiversity Atlas places the park within the Everglades, Big Cypress Swamp, and Mangrove and Coastal Glades subprovinces of the Atlantic Coastal Plain, a geologically young region on Cenozoic sediments (NPS Geodiversity Atlas). The oldest unit mapped at or near the park surface is the Pliocene Tamiami Formation, a fossil rich mix of carbonate and siliciclastic rock in the northwest of the park near Big Cypress; the Pleistocene Miami Limestone, once called Miami Oolite, is a white to orangish gray sandy limestone; and the Key Largo Limestone forms a regional band about 225 miles long that extends to North Miami Beach (NPS Geodiversity Atlas).

At the coast, the atlas lists young Holocene surface deposits: marl, marl over peat, quartz sands, carbonate sands and mud, and organic material (NPS Geodiversity Atlas). USGS adds that South Florida sits very close to sea level and that the shape of its coast changes over time (USGS Everglades geology).

Historically, water ran down the Kissimmee River into Lake Okeechobee and then south through the Everglades to Florida Bay as uninterrupted sheetflow (SFWMD Everglades).

The slope behind that flow is tiny. UF/IFAS Extension describes an elevation gradient from Lake Okeechobee to Florida Bay of less than 4.5 centimeters per kilometer, which spread a sheet of water about 48 kilometers wide across the peat; early measurements found water 15 centimeters to 1 meter deep, rarely stagnant and moving about 34 meters a day (UF/IFAS EDIS UW199). Historical records cited in the same publication suggest sloughs held water about nine months of the year, while some tree islands flooded for perhaps three months (UF/IFAS EDIS UW199).

At the southern edge, SFWMD describes Florida Bay as linked to the Everglades both by fresh water flowing into the bay and by salt water seeping into the Everglades (SFWMD Everglades). To the west, the National Park Service says the fresh waters of the Big Cypress Swamp are essential to the neighboring Everglades and feed the estuaries along Florida's southwest coast; Big Cypress National Preserve protects more than 729,000 acres of that swamp (NPS Big Cypress National Preserve).

Ridge and slough is the patterned marsh of the central and southern Everglades, where alternately spaced sawgrass ridges and sloughs line up closely with the original direction of flow (UF/IFAS EDIS UW199).

The UF/IFAS publication describes two main pre-drainage marsh landscapes, sawgrass plains in the north and ridge and slough in the center and south, with somewhat regularly spaced tree islands that made the marsh resemble a patterned peatland (UF/IFAS EDIS UW199). Peat surfaces on ridges and in sloughs differed by about 0.5 to 1 meter, and the original flow direction, the alignment of ridges and sloughs and the orientation of tree islands match closely (UF/IFAS EDIS UW199).

Those small differences matter. The National Park Service puts it plainly: in the Everglades, elevation is everything, and even a few inches can influence which ecosystems develop (NPS Everglades, Nature). The extension publication reports that shorter flooding periods and lower ground water have cost some areas between 1 centimeter and 1 meter of peat soil, flattening the ridges (UF/IFAS EDIS UW199).

Water levels and flow in the Everglades are now largely set by a system of levees and canals first built for flood control, land drainage and water supply (USGS Everglades geology and hydrology).

USGS warns that land subsidence caused by drainage and oxidation of peat soils will greatly complicate restoration and threatens the future of agriculture in the Everglades (USGS). SFWMD says canals, levees and roads have split the present Everglades and cut the central marsh off from adjacent transitional wetlands, and that impounding the Water Conservation Areas has overdrained some areas and flooded others (SFWMD Everglades). Everglades National Park and the Water Conservation Areas were designated Outstanding Florida Waters in 1978 (SFWMD Everglades).

The farm belt has a legal boundary too. Section 373.4592 defines the Everglades Agricultural Area by a metes and bounds description that begins at a section line meeting the Army Corps of Engineers Levee D-9 in Palm Beach County, and it separately defines the C-139 Basin by its own land description (section 373.4592, F.S.). The extension publication traces drainage back to the mid-1800s, when about 200 square kilometers north and west of Lake Okeechobee were ditched and drained for agriculture (UF/IFAS EDIS UW199). Restoration projects and the plants and animals of the marsh are covered on the statewide restoration and ecosystem guides.

Last verified: October 18, 2026, against the SFWMD Everglades page, section 373.4592 of the 2026 Florida Statutes, the NPS Geodiversity Atlas and park pages, two USGS pages and UF/IFAS publication UW199, each reloaded that day.