Flathead Lake Facts: Size, Depth and Water Level
Start with the science, then plan the lake day. These quick facts come from the University of Montana's Flathead Lake Biological Station, with a direct link for current lake levels rather than an old reading.
How big is Flathead Lake?
Flathead Lake covers 191.5 square miles of water surface. The Biological Station describes it as the largest natural freshwater lake by surface area in the western United States outside Alaska. That qualification matters: surface area, freshwater and the geographic comparison are part of the fact.
For a group trip, the useful next step is to choose a specific public access point and check its current rules. A lake-wide fact does not describe every beach, ramp or park.
How deep is Flathead Lake?
The maximum depth is 370.7 feet, according to the Biological Station. Its mean depth is about 164.7 feet. Maximum and average depth describe different things; neither tells you the depth at a particular swimming or boating spot.
The official facts page includes a bathymetric map, showing the shape and depth of the lake bottom. Use official information for your outing rather than treating one lake-wide number as a description of local conditions.
Where is Flathead Lake?
Flathead Lake is in Montana. The Biological Station's lake facts page includes a map with public access locations and identifies its own research center at Yellow Bay. Use that official map to understand the lake and the places you are considering.
The Tamarack is in Lakeside, near Flathead Lake's west shore. It is not lakefront and has no private or property-specific lake access. Choose a public beach, ramp or park for time by the water.
What is the current Flathead Lake water level?
Use the Biological Station's Weather Center for current and historical lake levels. This guide deliberately does not quote a live level: a copied number can be out of date by the time you plan your outing.
The facts page explains that lake levels change seasonally and that the lake's outflow is regulated by Seli’š Ksanka Qlispe’ Dam near Polson. Check the live source and the responsible park or operator for details that affect your plans.
A lake trip with a home base
Keep a little space in the itinerary for the lake and a little for the house. The Tamarack in Lakeside sleeps up to 10 in six bedrooms, with a kitchen for shared meals, a game room, private hot tub and sauna.
Check your accommodation dates, choose a public access point and confirm current conditions before the outing. The related guides below cover state parks, camping and a boat-access visit to Wild Horse Island.
Keep planning your lake stay
Questions travelers ask
How big is Flathead Lake?
Its water surface covers 191.5 square miles. The University of Montana's Flathead Lake Biological Station calls it the largest natural freshwater lake by surface area in the western United States outside Alaska.
How deep is Flathead Lake?
The maximum depth is 370.7 feet and the mean depth is about 164.7 feet, according to the Flathead Lake Biological Station.
Where is Flathead Lake?
Flathead Lake is in Montana. The Biological Station's official facts page includes a lake map with public access locations; its research center is at Yellow Bay.
Where can I check the current lake level?
Use the Flathead Lake Biological Station's Weather Center, linked on this page, for current and historical lake levels. This guide does not quote a live water level.
Make The Tamarack your Lakeside base.
Six bedrooms and 4.5 baths. Sleeps up to 10, near Flathead Lake.
Check dates & book directOfficial sources, verified Oct 27 2026
- University of Montana FLBS: Flathead Lake Facts
- University of Montana FLBS: Weather Center and lake levels
Conditions and details change. Check the official site before your visit for current access, rules, closures and other planning details.