The Kootenai River draws its headwaters from southeastern British Columbia, northern Idaho, and northwest Montana. The river originates in Kootenay National Park, near Banff, British Columbia, and flows south into Montana near Rexford, then through the Purcell and Salish mountains. In 1972 Libby Dam impounded the Kootenai River, transforming the upper 48 miles of the mainstem in Montana and 42 miles in Canada into its reservoir, Lake Koocanusa. Just below the dam, the Kootenai turns northwest to wind in the deep cleft between the Cabinet and Purcell mountains. Downstream 17 miles, near Libby, Montana, it flows through a single narrow channel and into a steep-sided canyon. Twelve miles farther on, the river cascades over a series of bedrock faults to form Kootenai Falls, the only remaining large, undammed falls in Montana. Just above the Falls, a series of rapids and falls alternate with pools 20 to 40 feet deep, and the river is over 300 feet wide. Below, the aquatic environment features vertical canyon walls along both shores with many small, glacially carved coves, a relatively narrow channel, and deep pools broken up abruptly by rapids and falls. Water depths exceed 80 feet. Within several miles, the canyon transitions into a valley restricted by steep, heavily timbered mountain slopes and the Kootenai River crosses into Idaho, 97 miles from its Montana entry point. It journeys 66 miles in Idaho to reenter Canada, and joins the Columbia River at Castlegar, British Columbia, 485 miles from its origin.