The Flathead River (Salish: člq̓etkʷ ntx̣ʷetkʷ, ntx̣ʷe, Kutenai: kananmituk),[6] in the northwestern part of the U.S. state of Montana, originates in the Canadian Rockies to the north of Glacier National Park and flows southwest into Flathead Lake, then after a journey of 158 miles (254 km), empties into the Clark Fork.

With a drainage basin extending over 8,795 square miles (22,780 km2) and an average discharge of 11,380 cubic feet per second (322 m3/s), the Flathead is the largest tributary of the Clark Fork and constitutes over half of its flow.

The 1846 settlement of the Oregon Boundary Dispute established the border with British North America and that the Flathead Valley was firmly American.

In 1988 the International Joint Commission, ruled that a proposed open pit coal mine would violate the 1909 Boundary Waters Treaty.

[citation needed] Energy development once threatened the North Fork, which was deemed the "wildest river in the continental United States" by The New York Times in 2004.

On February 21, 2008, BP announced to drop plans to obtain drilling rights for coalbed methane extraction in the river's headwaters.

[18] There is a proposal to protect one-third of British Columbia's Flathead River by adding it to the Waterton-Glacier International Peace Park.