With the rise of sea levels that occurred during the Pleistocene approximately 17,000 years ago, the runoff of water from Lake Okeechobee slowed and created the vast marshland that is now known as the Everglades. Slower runoff also created an accumulation of almost 18 feet (5.5 m) of peat in the area. The presence of such peat deposits, dated to about 5,000 years ago, is evidence that widespread flooding had occurred by then.[21]