The Mackenzie River is the largest north-flowing river in North America. It is the longest river in Canada and it drains a watershed that occupies nearly 20 per cent of the country. The river is big and complex.
It is also jurisdictionally intricate with tributary rivers running through three provinces – British Columbia, Alberta and Saskatchewan – two territories – Yukon and the Northwest Territories – and areas which fall under the jurisdiction of numerous independent indigenous governments. Large tributary rivers, the Liard, Peace and Athabasca drain much of north central Alberta and parts of the Rocky Mountains in northern British Columbia. The Peace and Athabasca Rivers flow to Lake Athabasca, which is drained by the Slave River, the primary feeder to Great Slave Lake. The Mackenzie River itself flows from Great Slave Lake to the Arctic and lies wholly within the Northwest Territories.