General Description

(Source: Biodiversity Institute of Ontario)

The Mackenzie River is the longest river in Canada covering a distance of around 1800 kilometers (km). It begins at Great Slave Lake in the Northwest Territories and flows north into the Arctic Ocean, discharging 306 cubic kilometers of water per year (including 100 million tons of sediment). It is the main stem of the second largest river system in North America (after the Mississippi-Missouri river system), and the fourth largest of all river systems discharging into the Arctic Ocean (the three largest are in Russia). The entire Mackenzie river system extends 4250 km and drains 1.8 million sq. km. It includes three major lakes (Great Slave, Great Bear and Athabasca) and numerous major rivers (such as the Peace, Athabasca, Liard, Hay, Peel, South Nahanni and Slave rivers). It spans four physiographic regions: Western Cordillera, Interior Plain, Precambrian Shield and Arctic Coastal Plain.

The Mackenzie River System. (Source: Biodiversity Institute of Ontario)

The Mackenzie River travels northeast across an extensive lowland, moving through mid-range boreal forest into the northern boreal forest and sub-alpine vegetation of the subarctic zone. In its middle section, the river is over 6 km wide as it moves through a region of low hills. At one point, called the "Ramparts," the channel narrows to less than 0.5 km and the river flows at high speed between 60-meter (m) high cliffs. Further north the Mackenzie becomes a broad meandering stream filled with shifting sands. The channel is ever-changing as the annual freeze up and sudden flood of water and ice scour the river bottom.

The Mackenzie's outlet in the Beaufort Sea is the site of an extensive delta. It is more than 160 km long and consists of a complex network of braided channels. The flat land is covered in sparse arctic and tundra vegetation and dotted with "pingoes." The latter are cone-shaped hills that result from permafrost (frozen ground) forced upward by pressure from subterranean water.

Human Impact

A lake in the delta. (Source: Biodiversity Institute of Ontario)

Much of the river valley sits on permafrost which is unsuitable for agriculture, construction or other industrial activities. It is thus a serious obstacle to economic development along the Mackenzie river. The Mackenzie has, however, been extensively modified for harnessing hydroelectric power. Eight large dams have been constructed with a total reservoir capacity of 75 cubic km. These dams have had significant effects on downstream ecosystems.

History and Culture

A pingo in the Mackenzie Delta. (Source: photo courtesy of Terrain Sciences Division, Natural Resources Canada)

The river was named after fur trader Sir Alexander Mackenzie, who in 1789 became the first European to travel down the Mackenzie from Lake Athabasca to the Arctic Ocean (he was actually trying to find a river leading to the Pacific Ocean). Many trading posts were later established along the river to tap the interior regions for fur.

Native peoples call the river Deh Cho, which means "Big River." The river continues to be a lifeline for peoples of five different cultures: Inuit, Inuvialuit, Dene, Metis and non-native Canadians. It serves as an important transportation route to the western Arctic and many communities depend on the "barge-trains" that travel along the Mackenzie during the summer.