Flathead Lakers Swim Guide

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

The Flathead Lakers’ approach is to encourage land and water stewardship, broaden the constituency for responsible and thoughtful land use planning and resource management, and build partnerships to more effectively address conservation priorities so that our communities can absorb growth and provide economic opportunities while maintaining the special natural heritage and quality of life for future generations.

The Flathead Lakers provides leadership and a strong voice for protecting and improving water quality through our programs and advocacy.

The Flathead Lakers have been involved in the Swim Guide since its introduction to Flathead Lake in 2018, by open water swimmer and coach Mark Johnston of  FLOW Swimmers . We sample and monitor the water quality of Flathead Lake’s swimming beaches to reduce the risk of water-borne illnesses due to open water swimming

The Flathead Swim Guide Project is a collaborative project between the Flathead Lakers, Flathead Lake Biological Station (FLBS), and the Confederated Salish and Kootenai Tribes. We provide weekly updates on water quality for 16 swimming locations around Flathead Lake.

You can find the locations and results for each beach at  The Swim Guide , or download the app for iOS or Android. The Swim Guide provides information on over 7000 swimming locations throughout the world. The Flathead Lake Biological Station supports the Swim Guide by testing the water samples taken from local swim beaches,

To learn more about the Flathead Lakers or Monitoring Montana Waters, click the caption below each organization's logo.