Provo, river, c.70 mi (110 km) long, rising in the Uinta Mts., NE Utah, and flowing SW past Provo to Utah Lake. It was early used for irrigation, but after Utah Lake was badly depleted in the 1930s, the Bureau of Reclamation rehabilitated the old irrigation installations and built new ones centering on the Provo River. The project also gets water from the Weber River by a canal (built 1929–30; enlarged 1941–47) and from the Duchesne River, a tributary of the Green River, by a tunnel (completed 1942) across the mountain divide. The water is used to irrigate the valley of Utah Lake and to supply the needs of the towns there; in addition, Salt Lake City is served by the 42-mi-long (68-km) Salt Lake Aqueduct (completed 1951). The Deer Creek Dam (completed 1941) is the chief dam on the Provo River; it impounds a large reservoir and has a power plant.