Wakulla-Leon Sinks cave system

The longest mapped underwater cave in the United States, about 45 miles (72 km) linking Wakulla Spring to the Leon Sinks area beneath the Woodville Karst Plain; mostly deep, explored by the Woodville Karst Plain Project, with very limited recreational access.

South of Tallahassee, rain and swamp water drain into the flat limestone country of the Woodville Karst Plain through sinkholes and sinking streams, flow through large water-filled tunnels and re-emerge at Wakulla Spring, one of the largest springs in the United States. Divers have mapped those tunnels for decades, and in December 2007 two divers swam from Turner Sink, in the Leon Sinks part of the network, to Wakulla Spring, proving that the two caves form one system.

The Woodville Karst Plain Project (WKPP), a non-profit exploration and research group, reported in 2023 that it had connected Chip's Hole cave to the system, bringing the surveyed total to 236,723 feet (about 44.8 miles, or 72 km). Florida State Parks gives the same order of figure and notes more than 30 known entrances and more than 22 miles of passage deeper than 190 feet (58 metres). Exploration here has depended on mixed breathing gases, underwater scooters and rebreathers, and several world distance records were set in these caves.

Recreational access is narrow. Scuba diving is not allowed in Wakulla Spring itself or its swimming area. Within Edward Ball Wakulla Springs State Park, certified cave divers may dive Emerald Sink and Clearcut Sink, although the park listed Clearcut as closed because of road construction on US Highway 319. In the Leon Sinks Geological Area of the Apalachicola National Forest, the Forest Service prohibits swimming, and WKPP history records that diving access was restricted after the sinks were included in the protected area in 1987.

The system matters well beyond diving. Dye-trace studies show water entering swallets (sinking streams) far upstream reappearing at Wakulla Spring, and WKPP teams collect water samples and radio-locate passages from the surface as part of their mapping work.

The caves lie in the Upper Floridan aquifer, mainly in the Oligocene Suwannee Limestone and the overlying Miocene St. Marks Formation. Inside the Wakulla Spring cave the top of the Suwannee Limestone is met at about 90 feet below the water surface, and the St. Marks Formation is exposed between about 9 and 90 feet. Florida's state geologist designated Edward Ball Wakulla Springs State Park a State Geological Site on 2018-12-20.

Wakulla Spring discharges roughly 300 million gallons a day from a watershed estimated at 975 square miles reaching into south Georgia. Part of that water is young surface water that sinks through large swallets and travels quickly through the conduits; dye traces have confirmed links from four major swallets to the spring. Florida State Parks says Wakulla has one of the largest observed ranges of discharge of any Florida spring.

The longest mapped underwater cave in the United States according to Florida State Parks. Mastodon and other Ice Age mammal bones have been recovered from the spring, including bones found just inside the cave mouth at about 220 feet in the 1950s. The 1987 US Deep Caving Team project tested an early fully closed-circuit rebreather here, and WKPP dives set distance-at-depth records in 2000, 2007 and 2008.

Florida State Parks counts more than 30 known entrances (sinkholes and springs). Recreational cave diving is published only for Emerald Sink and Clearcut Sink inside Edward Ball Wakulla Springs State Park (Clearcut listed as closed for road construction). Wakulla Spring is closed to recreational scuba; Leon Sinks entrances are on national forest land where swimming is prohibited; several other entrances are on private land.