Flathead Lake

Overview

Flathead Lake fills the valley between the Mission and Salish ranges south of Kalispell, the largest natural freshwater lake in the western United States outside Alaska. The Flathead Lake Biological Station puts it at 191.5 square miles, nearly 27 miles long and 15 wide, with a maximum depth close to 380 feet and a full pool of 2,893 feet. The Flathead and Swan rivers feed it, and the lake level is regulated at the south end by Seli's Ksanka Qlispe' Dam, the former Kerr Dam, on the lower Flathead River near Polson. It is so large and deep that most winters it never freezes over. The fishery is not what the old brochures describe. Kokanee were stocked in 1916 and became the region's famous fall run, but after Mysis shrimp reached the lake in 1981 the kokanee crashed and were gone by 1989, while lake trout thrived on the shrimp. Today lake trout, lake whitefish and yellow perch make up most of the catch, and the fish community looks more like the Great Lakes than a Rocky Mountain lake. Native westslope cutthroat and bull trout still use the lake and spawn in the North and Middle Fork tributaries, but cutthroat are catch-and-release and bull trout may not be fished for at all. The lake is split in two: FWP manages the north half, the Confederated Salish and Kootenai Tribes the south half, and the tribes host spring and fall Mack Days lake trout events sanctioned by FWP. For a fly rod that means streamers for lake trout when they are shallow, and cutthroat at the river mouths in spring, released where they are caught.