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. Lake Okeechobee sits in a shallow geological trough that also underlies the Kissimmee River Valley and the Everglades. The name Okeechobee comes from the Hitchiti words oki (water) and chubi (big), and means "big water". The oldest known name for the lake was Mayaimi (also meaning "big water"). The floor of the lake is a limestone basin, and the lake varies in depth from 1 to 13 feet (0.3 to 4 m). In 1926 the Great Miami Hurricane hit the Lake Okeechobee area, killing approximately 300 people. Two years later in 1928, the Okeechobee Hurricane crossed over the lake, killing thousands. In both cases the catastrophe was caused by flooding from a storm surge when strong winds drove water over the 6-foot (2 m) mud dike that circled the lake at the time.