Mackenzie River

• Category: Inland Aquatic Biomes.
• Geographic Location: North America.
• Summary: The Mackenzie River is the longest river and the largest watershed in Canada, with good ecological status and management, but subject to future climate and development challenges.

The Mackenzie River is named after the Scottish explorer Sir Alexander Mackenzie, while its indigenous Dene name is Deh Cho, meaning “big river.” It is the longest river in Canada, with the largest watershed, some 695,000 square miles (1.8 million square kilometers) draining one-fifth of the country. The river has the largest delta and the second-largest conglomeration of wetlands area in the country. Flowing through sparsely populated territory, it is one of the last pristine watersheds and ecosystems of the hemisphere.

Vital Arctic Flow

Beginning in Great Slave Lake, the 1,080-mile (1,738-kilometer) Mackenzie River flows north through the Arctic Circle to the Beaufort Sea. The watershed for the river is even greater, being over 2,600 miles (4,200 kilometers) long. The watershed begins with the Peace and Athabasca Rivers, gathers further waters from Lake Athabasca and the Great Slave Lake, and the Liard, Nahanni and Arctic Red Rivers. The watershed spans two provinces, Alberta and British Columbia, and two territories, the Northwest and Yukon Territories. All along its route and in the final delta, the Mackenzie River erodes, transports, and deposits sediments, creating a unique environment for many terrestrial, aquatic, and marine species.

The Mackenzie River discharges more than 78 cubic miles (325 cubic kilometers) of water each year, accounting for 11 percent of the total river flow into the Arctic Ocean. Due to such large volumes and seasonal discharges, the river has a significant impact on the climate of the Arctic Ocean, with large amounts of warmer freshwater mixing with the cold seawater. The highest flow occurs during the annual melt and breakup of ice and snow in June. The lakes and rivers of the Mackenzie and its tributaries are open, and flow from mid-June to the beginning of November. Despite this seasonal influence, annual flow is also considerable because water comes from the flat, barren shrubland tundra east of the river and the many large lakes in the watershed.

As it flows north, the Mackenzie River is a broad and slow-moving river. Its elevation drops just 512 feet (156 meters) from source to mouth. It is a braided river for much of its length, characterized by numerous sandbars and side channels. The river ranges from 1.25 to 3 miles (2 to 5 kilometers) wide, and is 26 to 30 feet (8 to 9 meters) deep in most parts. It is easily navigable by boat. The river ends in a wide fan-shaped delta of channels and islands where it empties into the Beaufort Sea lobe of the Arctic Ocean. The treeline narrows along the river, but never completely disappears, following the Mackenzie all the way to the delta, and representing the northern-most extension of boreal forest in Canada.

The Mackenzie Delta is a vast spread of low-lying alluvial islands, some 50 miles (80 kilometers) across, bordered on the west by the Richardson Mountains of the Yukon Territory, and in the east by the Caribou Hills of the Northwest Territories. In the delta, the river splits into three main navigable channels: an east channel, the west or Peel channel, and the middle channel where most of the water flows to the Beaufort Sea. The harbor in Tuktoyaktuk is a transfer point for ocean cargo, open from July to September.

Biota

The Mackenzie River and watershed is home to one of the largest and most intact ecosystems in North America. It is covered mainly by permafrost and tundra, wetlands, and boreal forests—most of which have never been logged. Tree species include dwarf birch, willow, alder, black spruce, lodgepole pine, tamarack, white birch, paper birch, quaking aspen, and balsam poplar.

Grasses and sedge are abundant in wetland areas, some of them pockmarked by peat bogs. Wildflowers thrive in the near-24-hour daylight of the short-lived summers here; species include Indian paintbrush, monk’s hood, sweet pea, yellow cinquefoil, purple crocus, blue Arctic lupine, and lousewort.

Fish species include the northern pike, lake whitefish, and coney among the freshwater types; and Pacific salmon, cisco and Arctic char among the anadromous ones.

Migratory birds use the two major deltas in the watershed basin—the Mackenzie Delta on the Beaufort Sea and the Peace-Athabasca Delta far inland—as important resting and breeding grounds. Tundra swan, snow goose, and black brant are frequently seen in great numbers at the 170-mile-long (270-kilometer-long) bird sanctuary based in the Mackenzie Delta. This area is also vital to beluga whales, many of which calve in these waters.

Barren-ground and boreal woodland caribou travel across the tundra and forests that surround the Mackenzie River, feeding mainly on lichen. Permafrost lies under as much as three-quarters of the watershed, which restricts its biological diversity somewhat. Other larger mammals here include grizzly and black bear, moose, musk-ox, and Arctic wolf. Among the well-established community of smaller mammals are muskrat, Arctic and red fox, and snowshoe hare.

Threats and Conservation

Although the Mackenzie River has not been dammed, many of its tributaries have been modified by dams for hydroelectricity, flood control and agriculture. Two major dams on the upper Peace River in British Columbia generate electricity and control flooding in that province, but also challenge the sustainability of wildlife and ecosystems along the entire Mackenzie River.

Future challenges and opportunities for the Mackenzie River biome include climate and environmental changes; proposed hydrocarbon, hydroelectric, and mining developments in the watershed; upstream diversions and impoundments of water, affecting rate and seasonality of flows; and the impact of transboundary airborne contaminants on the ecosystem. Cooperative management among the residents along the river and governments of the watershed areas will be necessary to encourage economic development while preserving this valuable ecosystem. The Dene, Inuvialuit, Métis, and non-Indigenous people inhabit the Mackenzie River and Delta, though it is quite sparsely populated with isolated settlements primarily linked by the river. With the resolution of northern land claims for the Northwest Territories in the 1980s and 1990s, Indigenous people in the regions have important rights to, and participation in, land and water management, environmental assessment, and economic development.

There are complex and multiple jurisdictions and water authorizations for the Mackenzie River and watershed under national, provincial, and territorial processes. Four land and water boards regulate the portion of the watershed located in the Northwest Territories: the Gwich’in Land and Water Board, the Sahtu Land and Water Board, the Wek’eezhii Land and Water Board, and the Mackenzie Valley Land and Water Board. The Mackenzie River Basin Board was created under the Transboundary Waters Master Agreement; it commits all authorities to manage watershed resources for ecological integrity in a sustainable manner for present and future generations. The Basin Board influences legislative and administrative decisions by providing reports on the state of the aquatic ecosystem.

Among reserves in the biome are three marine protected areas in the Mackenzie Delta area; these help to preserve beluga whale migration routes, bird breeding and molting areas, and freshwater and marine fish habitat.

Climate change effects in the Mackenzie River biome are already being recorded, particularly permafrost melt, changing water levels, and land subsidence (settling of the ground after water is excessively withdrawn from an aquifer). Warmer sea-surface temperatures have contributed to an increase in air temperature, and the warmer air penetrates into the permafrost layer that underlies much of the land in the Mackenzie watershed. This can disrupt local habitats by collapsing the soil structure and altering water flow; more broadly, it is known that melting permafrost releases greenhouse gases that then contribute to accelerated global warming—a positive feedback loop with negative consequences. Climate change has also created irregular weather patterns in the area, resulting in both drought conditions and times of extreme flooding. Beginning in 2022, drought in the area caused water levels to lower. As water levels continued to lower, government officials, including the US Coast Guard, warned users of the river to exercise caution when navigating. Such challenges may become more frequent with the continued threat of climate change.

Researchers note that the Mackenzie provides extensive ecological services—water filtration, carbon sink, snow albedo enhancer—that help to counter global warming and keep the Arctic Ocean region more stable. This is another reason why its protection as an intact ecosystem is of vital concern.

Bibliography

Alliston, W. George. A Monitoring Study of the Species, Numbers, Habitat Use and Productivity of Waterfowl Populations on Two Study Areas in the Wooded Mackenzie Delta, Summer 1983. LGL Ltd., 1985.

“Canadian Coast Guard Warns Mackenzie River Users of Low Water Levels.” Canadian Coast Guard, 4 July 2024, www.canada.ca/en/canadian-coast-guard/news/2024/07/canadian-coast-guard-warns-mackenzie-river-users-of-low-water-levels.html. Accessed 21 Oct. 2024.

Doyle, Alister, and Janet Lawrence. “Canada’s Mackenzie River Needs Aid as Climate ‘Refrigerator.’” Reuters, 3 Sept. 2012, . Accessed 21 Oct. 2024.

Forbes, D.L, et al. "Subsidence Drives Habitat Loss in a Large Permafrost Delta, Mackenzie River Outlet to the Beaufort Sea, Western Arctic Canada." Canadian Journal of Earth Sciences, 8 Mar. 2022, cdnsciencepub.com/doi/10.1139/cjes-2021-0127. Accessed 21 Oct. 2024.

Gummer, W. D., et al. “The Northern River Basins Study: Context and Design.” Journal of Aquatic Ecosystem Stress and Recovery, vol. 8, no. 1, 2000.

Lesack, Lance F. W. “River-to-Lake Connectivities, Water Renewal, and Aquatic Habitat Diversity in the Mackenzie River Delta.” Water Resources Research, vol. 46, no. 1, 2010.

 “Some Canadian Rivers at Risk of Drying Up.” WWF, 15 Oct. 2009, www.wwfca.org/?176681/Some-Canadian-rivers-at-risk-of-drying-up. Accessed 21 Oct. 2024.