Big Arm is located twelve miles north of Polson on the "big arm" of Flathead Lake. Big Arm State Park is the largest park on Flathead Lake and is less than five miles north of Big Arm on Highway 93. At twenty-eight miles long and 15 miles wide, Flathead Lake is the largest natural freshwater lake in the western United States. Flathead Lake's Big Arm Bay is a popular jump-off point to Wild Horse Island State Park. The Salish-Kootenai Indians once pastured their horses on Wild Horse Island to keep them from being stolen by other tribes. Enjoy swimming, fishing, sailing and boating on the beautiful Flathead Lake!