This is the lock which controls water flow from Lake Okeechobee. 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. 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.