S-308 is a lock in the Herbert Hoover Dike at Port Mayaca, and the origin of the St. Lucie Canal, which is the eastern section of the Okeechobee Waterway, the only navigable cross-Florida waterway in the state (the waterway goes through Lake Okeechobee, connecting the Gulf of Mexico at Fort Meyers, to the Atlantic at Port St. Lucie, north of West Palm Beach). The St. Lucie Canal opened in 1924, and has been enlarged twice since. There is another lock at the other end of the canal, 22 miles away, where it enters the estuary at Port St. Lucie, and connects at sea level.