The Columbia River Treaty is a 1964 agreement between Canada and the United States on the development and operation of dams in the upper Columbia River basin for power and flood control benefits in both countries. Four dams were constructed under this treaty: three in Canada (Duncan Dam, Mica Dam, Keenleyside Dam) and one in the United States (Libby Dam). The treaty provided for the sharing with Canada of one-half of the downstream U.S. power and flood benefits, and allows the operation of Treaty storage for other benefits. The long-term impacts of the treaty have been mixed: while the dams have provided enormous economic benefits to British Columbia and the U.S. Pacific Northwest through hydroelectric generation and flood control, there are longstanding concerns regarding social and economic impacts to the local communities, and the environmental effects associated with the construction and operation of large dams.