watercourse, south-central Idaho, U.S., that rises in the south slopes of the Sawtooth Range in the Sawtooth National Forest and flows south past Sun Valley, Ketchum, and Hailey, then west to join the Snake River near Gooding after a course of about 129 miles (208 km). Magic Reservoir, impounded just above Shoshone Ice Caves, is used for irrigation. The scenic river drains an area of about 3,070 square miles (7,951 square km) and includes some of Idaho's most productive trout streams.