South Fork Flathead River, Mountain brook in Bob Marshall Wilderness Complex, Montana, United States

The South Fork Flathead River begins where Danaher Creek and Youngs Creek meet between the Flathead Range and the Swan Range, south of Glacier National Park. It runs about 98 miles north-northwest, meandering for some 40 miles through a forested, undeveloped valley before entering a narrow gorge and then the backwater of Hungry Horse Reservoir, which covers 97 square miles.

The waterway held importance for Native American tribes who settled along its banks and relied on it for their livelihoods. When European settlement arrived in the 1800s, usage patterns shifted, and the river later received protection as a National Wild and Scenic River in the 1970s.

The South Fork's name comes from the Flathead River, which the Salish and Kootenai peoples knew long before settlers arrived. The river's upper 40 miles flow through the Bob Marshall Wilderness, where pack trains and hikers still follow trails without bridges or motor access. Its cutthroat trout population is isolated by Hungry Horse Dam, completed in 1953, which blocks upstream migration.

Visitors need wilderness permits and should prepare for multi-day journeys requiring either backpacking or horse travel through mountain trails. Summer months offer better access and more favorable conditions for outdoor travel compared to winter weather and snow.

The river harbors an isolated population of pure-strain cutthroat trout protected by its remote location from mixing with other species. Strict fishing regulations on catch limits help maintain this distinction and draw anglers seeking a special experience.