River, southeastern British Columbia, Canada, and western Montana, U.S. Rising in the MacDonald Range, it flows south for 240 mi (385 km) across the Canada-U.S. boundary into Montana.
After passing between the Whitefish Range and Glacier National Park , it enters Flathead Lake and emerges to join the Clark Fork . The Flathead valley is a resort region with diversified farming and fruit growing, lumbering, and mining.