Completed in 1941, Grand Coulee Dam was the world's largest concrete structure and remains so today. President Franklin D. Roosevelt supported damming the Columbia River as a massive federal project that put people to work during the Great Depression of the 1930s while also promising huge amounts of electricity and water to irrigate over a million acres of new farmland. Officials regarded the loss of salmon runs and riverside communities as unfortunate but necessary costs. Over eight years, thousands of workers mined sand and gravel, polished bedrock for the foundation, froze hillsides to prevent slides, poured millions of yards of concrete, and installed generators to produce electricity. Finished as the United States entered the Second World War, the dam's electricity powered critical wartime industries. Irrigation began in the early 1950s, when water was pumped through huge tubes from Roosevelt Lake behind the dam to Banks Lake on the plateau above. Grand Coulee Dam is operated by the Bureau of Reclamation, U.S. Department of the Interior.