The Flathead River (, , ), 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 , empties into the Clark Fork. The river is part of the Columbia River drainage basin, as the Clark Fork is a tributary of the Pend Oreille River, a Columbia River tributary. With a drainage basin extending over and an average discharge of , the Flathead is the largest tributary of the Clark Fork and constitutes over half of its flow. Course The Flathead River rises in forks in the Rocky Mountains of northwestern Montana. The largest tributary is the North Fork, which runs from the Canadian province of British Columbia southwards. The North Fork is sometimes considered the main stem of the Flathead River. Near West Glacier the North Fork combines with the Middle Fork to form the main Flathead River. The river then flows westwards to join the South Fork and cuts between the Whitefish Range and Swan Range via Bad Rock Canyon. All of the headwaters forks are entirely or in part designated National Wild and Scenic Rivers. After the river leaves the canyon it flows into the broad Flathead Valley and arcs southwest, passing Columbia Falls and Kalispell, before it is joined by the Stillwater River and its Whitefish River tributary, and then empties into Flathead Lake, where the Swan River joins. Near Polson the river leaves the natural basin of Flathead Lake, but first passes through Seli’š Ksanka Qlispe’ Dam (formerly Kerr Dam), which raises Flathead Lake's level by 10 feet. After flowing through the dam the river turns south and meanders through the Flathead Valley west of the Mission Mountains, and at Dixon it is joined by the small Jocko River. At the Jocko River confluence it turns west, and a few miles after flows into the Clark Fork near Paradise. History David Thompson (explorer) first explored the area in 1807. Fur traders employed by the North West Company and Hudson's Bay Company entered the Flathead Valley in the early 19th century. Trading posts were established north of Flathead Lake. The 1846 settlement of the Oregon Boundary Dispute established the border with British North America and that the Flathead Valley was firmly American. The first settlers began arriving in the 1860s. Irrigation agriculture began in