Grand Coulee Dam south, enclosed and created Banks Lake, which covered the northern of the Grand Coulee. Additional dams, such as the Pinto and O'Sullivan Dams, were constructed alongside siphons and canals, creating a vast irrigation supply network called the Columbia Basin Project. Irrigation began between 1951 and 1953 as six of the 12 pumps were installed and Banks Lake was filled. After World War II, the growing demand for electricity sparked interest in constructing another power plant supported by the Grand Coulee Dam. One obstacle to an additional power plant was the great seasonality of the Columbia River's streamflow. Today the flow
Grand Coulee Dam residents were relocated. The Anti-Speculation Act was passed in 1937, limiting the amount of land farmers could own to prevent inflated prices. The government appraised the land and offered to purchase it from the affected residents. Many refused to accept the offers, and Reclamation filed condemnation suits. Members of the Colville Confederated and Spokane tribes who had settlements within the reservoir zone were also resettled. The Acquisition of Indian Lands for Grand Coulee Dam Act of , 1940, allowed the Secretary of the Interior to acquire land on the Colville and Spokane Reservations, eventually accounting for . By 1942, all