The Koyukuk River 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.
