Wild Horse Island

Wild Horse Island is the largest island in Flathead Lake, the largest freshwater lake in Montana. For centuries, the Salish-Kootenai used the 2,100 acre (8.5 km²) island to pasture horses to keep them from being stolen by other tribes. Protected as a state park since 1978, the island near Big Arm Bay is home to abundant wildlife including bighorn sheep, mule deer, waterfowl, bald eagles, and at least three wild horses. Access is by boat only and for day use only. It is managed by the Montana Fish, Wildlife & Parks.

More info at  en.wikipedia.org