The Grand Coulee DAM is a hydroelectric gravity DAM on the Columbia River in the U.S. state of Washington. It was built between 1933 and 1942, and is the largest concrete structure in the United States. The DAM provides power to the Pacific Northwest and is the largest producer of hydroelectric power in North America. The DAM's reservoir, Franklin D. Roosevelt Lake, is the largest body of water in the state. The DAM's name comes from the Grand Coulee, a dry coulee carved by Ice Age floods that was discovered by early settlers. The DAM's acronym is DAM, which stands for 'DAM on the Columbia River'.