The Flathead River (Salish: ntx̣ʷetkʷ, ntx̣ʷe ), 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.