Exploring our Lake and Watershed

Flathead Lake is the largest freshwater lake west of the Mississippi River. It is almost 28 miles long and up to 15 miles wide with a maximum depth of 370 feet.

It is one of the cleanest lakes of its size and type anywhere in populated areas of the world. The clarity of Flathead Lake’s waters is renowned. In the summer it is often easy to see through twenty feet of the water column. The lake is so clear because it is relatively low in nutrients (phosphorus and nitrogen) which promote the growth of algae.

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 jointly manage fisheries in the lake with the state of Montana’s Department of Fish, Wildlife and Parks.

The lake is inhabited by native bull trout and cutthroat trout. Fisherman seek trophy-size lake trout, yellow perch, and lake whitefish in its waters.

Local legend even tells of a creature rivaling ‘Nessie’ residing in its depths.

Wildlife and birds are abundant, inhabiting the lake’s shores and islands.

Wildhorse Island, at 2,170 acres, is the largest island in the lake. Most of the island is managed for wildlife by the Department of Fish, Wildlife and Parks. Its name comes from its history as a refuge for a local tribe’s horses when raiding tribes ventured into the area. A few wild horses can still be found here along with bighorn sheep and deer.

A wildlife refuge managed by the U.S. Fish and Wildlife Service is located on the north shore of the lake. Six state parks are scattered along the lake’s shores, offering opportunities for boating, sailing fishing, camping and swimming.

Those of us who live or visit here treasure the special natural, recreational, spiritual and economic values Flathead Lake and its tributaries provide.

A watershed is an area of land that drains into a particular stream or river. It is also called a drainage basin or catchment.

The Flathead Watershed includes all the land that drains into Flathead Lake and the Flathead River – a huge area stretching west from the Continental Divide to the Salish Mountains and from across the Canadian border in the north to the Clark Fork River in the south. The Flathead Watershed contains many smaller watersheds.

Water flows from pristine headwaters in Glacier National Park, the Bob Marshall Wilderness and other wild lands, through forests, farms, and cities. The waters of the Flathead, Stillwater, Whitefish, and Swan rivers all join in Flathead Lake, the largest natural freshwater lake west of the Mississippi River. Altogether, the Flathead Watershed drains six million acres of scenic landscapes.

Rivers

The Flathead River is the largest tributary of the Clark Fork River and headwaters of the Columbia River.

Headwaters in the mountains and protected areas help sustain fish and wildlife and clean water in the watershed. The Flathead National Forest administers the largest amount of public land in the watershed, approximately 60% of forested lands in the North, Middle and South Forks of the Flathead, and the Swan and Stillwater drainages. Recharge areas found in Glacier National Park, the Bob Marshall Wilderness and other undisturbed forested lands provide clean water to the rivers and lakes of the watershed.

The three forks of the Flathead River contribute about 85% of the water entering Flathead Lake. Flows into and through the lake are partially controlled by Hungry Horse Dam on the South Fork of the Flathead River and Kerr Dam near the lake’s outlet.

The large valleys of the watershed were scoured by recurring glaciers, leaving a trail of alluvial (gravel, sand, silt and clay) and outwash (gravel and sand mixture) deposits and glacial till (materials of all sizes pushed by advancing glaciers). Many lakes, wetlands and floodplains were formed by the glaciers.