Flathead is the largest natural freshwater lake in the western United States. Twenty eight miles long and 15 miles wide, Flathead Lake is renowned for its fishing. Wild Horse Island, a 2,163 acre wilderness area on the west shore of the lake, is home to bald eagles, bighorn sheep, and wild horses.

On Flathead Lake's Big Arm Bay, this park is a popular jump-off point to Wild Horse Island. Big Arm's long pebble beach is popular with sunbathers and swimmers. Camping under a stand of mature ponderosa pine and juniper is a major attraction. Others include: fishing for lake trout, board sailing, bird watching, scuba diving, swimming and water-skiing. This site is 2,967 feet in elevation and has encompasses 55 acres. The park has both flush and vault toilets, grills/fire rings, firewood, picnic tables, trash cans, drinking water, and seasonal interpretive programs. A golf course and three museums are located in nearby Polson. RV/trailer size is limited to 30 feet in the 29 sites. There are also 6 tent sites available. The Big Arm unit of Flathead Lake State Park now has the latest in circular camping comfort, a 20 feet wide, 10 feet tall yurt. You need only bring bedding, cooking utensils, personal toiletries, a flashlight and a container for water. Electrical outlets, lights, electric heat and a propane barbecue for outdoor cooking are also provided. A joint state/tribal fishing license is needed for fishing at this park and campers may stay only 7 days during a 30 day period.