The Nelson river travels 644 km northward from Lake Winnipeg to Hudson Bay. Its total drainage area covers over 800 000 sq. kilometers (km) and it discharges 110 cubic km annually. It provides an outlet for the great Saskatchewan river system from Lake Winnipeg, with the two systems together (including the Bow River) traveling 2600 km and draining 1.2 million sq. km of land.
The Nelson's upper reaches are largely made up of interconnecting lakes (such as Cross Lake and Sipiwesk Lake) connected by falls and rapids. This irregular upper section does not have a defined river valley. After Split Lake, the Nelson is joined by the Grass and Burntwood tributaries and flows northeast across a flat forested lowland to the Hudson Bay.
The first European to explore the Nelson was Sir Thomas Button in 1612. The river was of great importance to the Hudson Bay Trading Company as a transport route. The Company established Fort Nelson at the river mouth in 1682 and York Factory a few kilometers south in 1684. The fur canoes were the only European vessels traveling the river until the 19th century, at which point the supplies and wheat exports of the new prairie settlers led to the further development of the river as a transportation route. Today the mighty Nelson powers two large hydroelectric facilities, one at Kettle Rapids and the other at Grand Rapids.