The 1,450 mile long Colorado River is one of the principal rivers of the Southwestern United States and northern Mexico. Known for its dramatic canyons, whitewater rapids, and eleven U.S. National Parks, the Colorado River system is a vital source of water for 40 million people in southwestern North America. The river and its tributaries are controlled by an extensive system of dams, reservoirs, and aqueducts, which in most years divert its entire flow for agricultural irrigation and domestic water supply. The Colorado's large flow and steep gradient are used for generating hydroelectric power, and its major dams regulate peaking power demands in much of the Intermountain West. Intensive water consumption has dried up the lower 100 miles (160 km) of the river, which has rarely reached the sea since the 1960s.