Flathead Lake Montana:
Flathead Lake is one of the 300 largest natural lakes in the world
and is the largest natural freshwater lake in the western United States. Of
those large lakes, Flathead is one of the cleanest. Studies at the Flathead
Lake Biological Station show that water quality in Flathead Lake is among the
best in the world. Flathead Lake's major tributaries are the Flathead and Swan
Rivers.
Located in the northwest corner of the state, 7 miles south of Kalispell, it is nearly 30 miles (44 km) long, 16 miles (25 km) wide, and covers 197 square miles (510 square km). Formed by the glacial damming of the Flathead River, the lake is bordered on its eastern shore by the Mission Mountains and on the west by the Salish Mountains. Once known as Selish Lake, the lake takes its name from the Salish (Flathead) Indians who live on the Flathead Indian Reservation located at the southern end of the lake. Kerr Dam, near Polson, regulates the lake's water level and provides hydroelectric power and water for irrigation.
Kerr Dam is located at the outlet of Flathead Lake in Polson, at the southern end. Regulation of outflow by the dam maintains the Lake's level between 2,883 and 2,893 feet above sea level. If runoff conditions in the mountains don't warrant flood threats, the Lake level is brought to 2,890 feet by the end of May and to full pool by June 15. Maximum flow in the Flathead River generally occurs during spring freshet between May 15 and June 10, creating a plume of sediment that covers the Lake surface.
Due to its massive volume and normally active winds over the surface, Flathead Lake does not freeze over most winters, although the bays often have winter ice cover. The Lake did freeze over in the winters of 1978-79 (all winter), 1987-88 (all winter), 1988-89 (March only) and 1989-90 (January only). Open space on the shoreline includes the National Wildlife Refuge on the North Shore and State land managed by the Flathead Lake Biological Station as a refuge on the South Shore (Polson Bay).