Nelson, river, c.400 mi (640 km) long, issuing from the northeast end of Lake Winnipeg, central Man., Canada, and flowing NE to Hudson Bay at Port Nelson. With the Bow–South Saskatchewan–Saskatchewan river system, which enters NW Lake Winnipeg, the Nelson is part of a 1,600-mi (2,575-km) continuous stream from W Alberta to Hudson Bay. There are hydroelectric plants at Kettle Rapids, Long Spruce, and Kelsey. Nickel-mining and -refining operations at Thompson use electricity generated by the river. The Nelson's mouth was explored (1612) by Sir Thomas Button. The river was long followed by fur traders; from 1682 to 1957 the Hudson's Bay Company maintained a trading post at York Factory on Hudson Bay.