Flathead Lake

Flathead Lake is almost 28 miles (45 km) long, 15 miles (24 km) wide in some areas, and has depths of up to 370 feet (113 m). One of the 300 largest lakes in the world, it has a surface area of 126,000 acres (50,990 hectares) when full. The depth of the lake varies by 6.6 to 9.8 feet (2 to 3 m) based on the activities of Kerr Dam. The average residence time, or time that water spends in the lake, is 2.2 years. Flathead Lake is one of the clearest and cleanest lakes in the settled world because it remains relatively low in the nutrients (phosphorus and nitrogen) that promote the growth of algae. The primary native fish species in the lake include bull trout, westslope cutthroat trout, and mountain whitefish. Introduced species include lake trout, lake whitefish, and yellow perch. The southern half of the lake is on the Confederated Salish and Kootenai Tribes’ Flathead Indian Reservation. The Tribes manage water quality on the reservation and join the state of Montana’s Department of Fish, Wildlife and Parks to jointly manage fisheries in the lake.

Figure 1.3: Flathead Lake. Source: Paul Frederickson


The water quality of Flathead Lake reflects how sustainably we are living within our environment and is a barometer of the ecological health of the entire Flathead Watershed. Our quality of life, well-being, and economic vitality depend on clean water and healthy ecosystems. It is therefore in the interest of all citizens of the Flathead Watershed to learn what our watershed has to offer, to understand the demands and pressures that our growing community places on the watershed, and to protect it for future generations.

For more information, send email to info@flatheadwatershed.org or info@flatheadcore.org.
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