Wild Horse Island is the largest island on Flathead Lake, the largest freshwater lake in Montana. For centuries, the Salish-Kootenai used the island, approximately in size, in order to pasture horses and keep them from being stolen by other tribes. The island was part of the Flathead Indian Reservation from the time of its creation in 1872 up until its dismantlement in 1904, when the island was divided into individual plots of land. A number of attempts were made on the island towards agricultural development, but none succeeded. Between 1910-1915, homesteaders on the island cut down much of the old growth trees and introduced non-native grasses and other plant species. These species have competed with and overtaken much of the short-grass prairie that herbivorous wildlife need to survive. This short grass prairie is one of the last few remaining in Montana, and because of this efforts must be made to control various animal species on the island in order to preserve the grasses from over-pasturing and extinction. Bighorn Sheep, for example, are managed at around 100 sheep. In 2014, the population was between 160-200 sheep, and Montana Fish, Wildlife, & Parks worked to relocate 59 sheep to other herds in Northwest Montana. Three of the top five bighorn sheep recorded by the Boone and Crockett Club during the three years 2015-2018 came from Wild Horse Island in Montana. In December, 1887, Theodore Roosevelt proposed the formation of the Boone and Crockett Club at a dinner at his residence in New York City, primarily for maintaining a scoring and data collection system by which native North American big game animals are measured and tracked as a gauge of successful wildlife management. Protected as a state park since 1977, the island near Big Arm Bay is home to abundant wildlife including bighorn sheep, mule deer, waterfowl, and bald eagles. , the wild horse population was five mares and one gelding. Access is by boat only and for day–use only. It is managed by Montana Fish, Wildlife & Parks and lies within both the Flathead Indian Reservation and Lake County, Montana. There are 56 private lots on the island, about each. The highest point is at, which is above the island's shores.
Climate and topography
A study conducted over a 25-year span has shown the average yearly precipitation on Wild Horse Island to be. The average daily temperature ranges from, with spikes sinking below during colder months and afternoons above during the hotter months in dryer years. Overall, the island experiences below freezing temperatures about two thirds of the year. Wild Horse Island was formed by the Cordilleran Glacier, giving the island a varying topography. Its shores are above sea level. The glacier caused the six summits in the center of the island, ranging in heights between, to be formed into rôche moutonnée, with rugged northern faces and rugged southern cliffs. Meadows sprawl the western and southern shores, while grasslands cover the southeast. The northern side of the island has forests of Ponderosa pine and Douglas fir trees.
