Lake Okeechobee 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 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, the wetlands built up the layers of peat rapidly enough (reaching thick) to
Lake Okeechobee Lake Okeechobee Lake Okeechobee (), also known as Florida's Inland Sea, is the largest freshwater lake in the state of Florida. It is the ninth largest natural freshwater lake in the United States and the second largest natural freshwater lake (the largest being Lake Michigan) contained entirely within the contiguous United States. Okeechobee covers , 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 . The lake is divided between Glades, Okeechobee, Martin, Palm Beach, and Hendry counties. All five counties meet at