By the mid-1960s, many rivers in the United States had been dammed or otherwise manipulated for flood control, recreation, and other water development projects. There was a growing concern that rivers in their natural state would soon disappear. By 1988, for example, roughly 17% (600,000 mi [965,400 km]) of all the previously free-running rivers in the United States had been trapped behind 60,000 dams.

The Klamath River in northern California, designated a wild river under the Wild and Scenic Rivers Act. (Visuals Unlimited. Reproduced by permission.)

In 1968, Congress passed the Wild and Scenic Rivers Act, establishing a program to study and protect outstanding, free-flowing rivers. Federal land management agencies such as the Forest Service and the National Park Service (NPS) were directed to identify rivers on their lands for potential inclusion in the National Wild and Scenic Rivers System. In 1982, the NPS published the National Rivers Inventory (NRI), a list...