Glen Canyon Dam, 710 ft (216 m) high, 1,560 ft (475 m) long, NE Ariz., on the Colorado River. The key unit of the U.S. Bureau of Reclamation's Colorado River storage project, it is one of the world's largest concrete dams (larger in bulk, though not in height, than Hoover Dam). The dam, completed in 1963 and dedicated in 1966 after completion of its power-generation facilities, regulates the flow of the upper Colorado and its tributaries and produces hydroelectricity (since 1964). The dam sharply reduced the seasonal flow of the Colorado downstream, dramatically altering the ecology of the river in the Grand Canyon. Changes in water releases have been experimented with in an attempt to ameliorate the effects of the dam.
Lake Powell, formed by the dam, extends 186 mi (299 km) upstream into S Utah. The lake was named after the American explorer John W. Powell, who mapped and named the canyon in 1870. This lake is the nucleus of the Glen Canyon National Recreation Area (see National Parks and Monuments, table). Downstream is the Glen Canyon Bridge, 1,271 ft (387 m) long and 700 ft (213 m) high, one of the world's longest and highest steel-arch bridges.