Okeechobee Mudfest, Florida, United States

Lake Okeechobee, locally referred to as The Lake or The Big O, is the largest freshwater lake in the state of Florida. It is the seventh largest freshwater lake in the United States and the second largest freshwater lake contained entirely within the lower 48 states. Okeechobee covers 730 square miles (1,900 km2), approximately half the size of the state of Rhode Island, and is exceptionally shallow for a lake of its size, with an average depth of only 9 feet (3 m). The lake is divided between Glades, Okeechobee, Martin, Palm Beach, and Hendry counties. Maps of Florida show that all five of these counties meet at one point near the center of the lake.
History
Lake Okeechobee sits in a shallow geological trough that also underlies the Kissimmee River Valley and the Everglades. The trough is underlain by clay deposits that compacted more than the limestone and sand deposits did along both coasts of peninsular Florida. Until about 6,000 years ago, the trough was dry land. As the sea level rose, the water table in Florida also rose, and rainfall increased. From 6,000 to 4,000 years ago wetlands formed in much of what is now the lake, building up peat deposits. Eventually the water flow into the area created a lake, drowning the wetlands. Along what is now the southern edge of the lake, however, the wetlands built up the layers of peat rapidly enough (eventually reaching 13 feet (4.0 m) to 14 feet (4.3 m) thick) to form a dam, holding back the water in the lake until it rose high enough to the flow over the shore into the Everglades. At its capacity, the lake holds 1 trillion gallons (1,000,000,000,000) of water and is the headwaters of the Everglades.