Lower Granite Dam, Lower Granite Lake, and associated facilities are operated for Hydropower, Navigation, Fish & Wildlife, Recreation, Water Quality, and Irrigation. Lower Granite Lock and Dam was the fourth of four dams constructed as part of the Lower Snake River Project, authorized in the Rivers and Harbors Act of 1945. Construction began in 1965 and three turbine units were operational in 1975. Three more turbine units were installed and operational in 1979. Lake Lower Granite extends from the dam upstream for 40 miles to Lewiston, Idaho. The Corps constructed roughly 8 miles of levees around Lewiston, ID, to help protect lives and property from potentially destructive high water conditions.