The Koyukuk River (; Ooghekuhno' in Koyukon, Kuuyukaq or Tagraġvik in Iñupiaq) is a 425-mile (684 km) tributary of the Yukon River, in the U.S. state of Alaska. It is the last major tributary entering the Yukon before the larger river empties into the Bering Sea. Rising at the confluence of the North Fork Koyukuk River with the Middle Fork Koyukuk River, it flows generally southwest to meet the larger Yukon River at Koyukuk. The river, with headwaters above the Arctic Circle in the Endicott Mountains of the Brooks Range, drains an area north of the Yukon River that includes part of the Gates of the Arctic National Park and Preserve, as well as Kanuti National Wildlife Refuge and Koyukuk National Wildlife Refuge. The main stem of the river is lined by the communities of Evansville, Bettles, Alatna, Allakaket, Hughes, and Huslia before reaching Koyukuk. Its headwaters tributaries include the Koyukuk's south, middle, and north forks, the Alatna River, and the John River. Major tributaries further downstream include the Kanuti, Batzu, Hogatza, Huslia, Dulbi, Kateel, and Gisasa rivers. Of these, the Alatna, John, and North Fork are National Wild and Scenic Rivers, as is the Tinayguk River, a tributary of the North Fork.
