The Fort Nelson River, often shortened to simply the Nelson River, is in north-eastern British Columbia, Canada. It flows 517 kilometres (321 mi) generally north-westward to the Liard River, a tributary of the Mackenzie River, which empties into the Arctic Ocean. The river drains a watershed of 55,900 square kilometres (21,600 sq mi) and is formed by the confluence of the Fontas River flowing from the east, and the Sikanni Chief River flowing from the south. These, along with the Sahtaneh and Muskwa Rivers, constitute the major tributaries. The source of the Sikanni Chief, on the eastern slope of the Rocky Mountains, is ultimately the headwater of the Fort Nelson River.