Colorado–Big Thompson project, constructed by the U.S. Bureau of Reclamation to divert water from the headstreams of the Colorado River to irrigate c.720,000 acres (291,400 hectares) of land in NE Colorado and to supply power; built 1938–56. Water is diverted by several dams, notably Granby Dam on the Colorado and Green Mt. Dam on the Blue River. Water is stored in Granby Reservoir, Shadow Mt. Lake, and Grand Lake before it is pumped through the Alva B. Adams Tunnel (13 mi/21 km long), to fall down the eastern slope of the Continental Divide into the Big Thompson River, a tributary of the South Platte. Dams near Fort Collins and Estes Park divert the water for use. Flatiron, Estes, Pole Hill, and Green Mt. dams generate hydroelectric power.