Fort Peck Dam, 21,430 ft (6,531 m) long and 250 ft (76 m) high, on the Missouri River, NE Mont.; one of the world's largest earth-filled dams. The dam was built (1933–40) by the U.S. Army Corps of Engineers as a flood-control and navigation-improvement project. In 1944 it became part of the Missouri River basin project and is used for irrigation and the generation of hydroelectricity. Fort Peck Lake, 189 mi (304 km) long, is one of the largest artificial lakes in the United States and an important recreation area of the N Great Plains.