Flathead Lake

Flathead Lake is the largest natural body of freshwater by surface area in the western United States, in the words of Montana Fish, Wildlife & Parks, which gives its size as about 191 square miles. It is roughly 30 miles long and up to 16 miles wide, reaches about 370 feet at its deepest, and lies between the Mission Mountains to the east and the Salish Mountains to the west, a few miles south of Kalispell. Polson sits at the south end, Bigfork near the northeast corner, and two highways circle it: US-93 on the west shore and MT-35 on the east.

The lake is a remnant of the last ice age. A glacier moving down the Rocky Mountain Trench stalled near present-day Polson and left a huge moraine that still holds the water in. The lake's outlet is dammed just below Polson; the dam, long known as Kerr Dam, has been owned by the Confederated Salish and Kootenai Tribes since 2015 and controls the top 10 feet of the lake. The southern half of the lake lies within the Flathead Indian Reservation. The lake moderates the local climate enough for the cherry orchards along the east shore and vineyards on the west.

Most visitors come for the water itself: boating, sailing, paddling and swimming from the state park beaches, where the water is known for its clarity. Flathead Lake State Park has six units: Big Arm, Finley Point, Wayfarers, West Shore, Yellow Bay and Wild Horse Island, the largest island in the lake, which is reached only by boat. Big Arm, Finley Point and Yellow Bay are on reservation land. Fishing in the southern half needs a Flathead Reservation tribal permit; the 2026-27 south-half license costs $19 plus fees for nonmembers.

Bringing a boat takes planning. Any watercraft coming into the Flathead Basin from outside it must be inspected for aquatic invasive species before launching, nonresidents need a Montana Vessel AIS Prevention Pass ($30 motorized, $10 non-motorized in 2026), and boats must stop at every open inspection station they pass. Lake levels depend on the dam and on drought; in the dry summer of 2023 abnormally low water hurt lakeside businesses and made navigation harder.

Practical tip: the wind can rise fast on an afternoon. Check the National Weather Service forecast for Flathead Lake before taking a small boat or paddleboard far from shore.