Within the boundaries of Mammoth Cave National Park, 25 miles of the Green River and six miles of the Nolin River carry boaters past dramatic bluffs, majestic trees, and wildlife. The Green River, dotted with sandbars, islands, and subsurface springs, averages 200 feet wide and 10 feet deep, though its depth may be much greater in places. The Nolin River also averages about 10 feet deep, but its channel is narrower than the Green River. When the rivers flood, however, the current can be very swift, but no whitewater conditions exist in the park. Regardless of water level, always be alert to numerous hazards such as submerged trees and rocks, drifting debris, and the park's ferry.