In 1869, John Wesley Powell led an expedition down the Green and Colorado Rivers in a bold attempt to explore the Grand Canyon for the first time. After, they told of raging rapids, constant danger, and breathtaking natural beauty of the American landscape at its most pristine. Retracing Powell's journey in 2008, Jon Waterman finds a parched river, one that millions of people depend upon. Exploring the causes and effects firsthand, Waterman also consults scientists and conservationists to better understand how to prevent an imminent catastrophe.