The river rises in southern Mount Rainier National Park, fed by the Nisqually Glacier on the southern side of Mt. Rainier. It flows west through Ashford and Elbe along Route 706. It is then impounded for hydroelectricity by the Alder Dam, completed in 1944, and the LaGrande Dam, completed in 1912 and rebuilt in 1945. They hold back Alder Reservoir and the inaccessible two-mile long LaGrande Reservoir. Before the construction of the dams, a natural fish barrier prevented anadromous fish from ascending the Nisqually above what is now La Grande Reservoir.