Do not be a victim of drowning! U.S. Coast Guard Approved personal flotation devices are required on the rivers in Mammoth Cave National Park. Drowning is the #1 cause of death in National Parks. Swimming in open, natural waters is very different from swimming in pools. Natural waters can change in depth unexpectedly, going from shallow to deep in just a few steps. Natural waters can also have swift currents and underwater hazards such as trees and rocks. Moving water is more powerful than the strongest swimmer. It is also deceptive and dangerous. Do not let moving water fool you. Even wading in shallow water can pull you off of your feet. Stay far enough back from moving water so that an accidental trip or slip on wet rocks will not cause you to fall into the current and be swept away.