The Grand Coulee Dam, opened in 1942, is one of the most massive concrete structures in the world. Located on the Columbia River in Washington State, it is 0.8 miles (1.3 km) long and 550 feet (168 m) high. It is a gravity dam that serves what was once the world's largest hydroelectric complex. The dam's reservoir, Roosevelt Lake, stretches 150 miles (241 km) toward the Canadian border.