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Mackenzie River
The Mackenzie River (Slavey language: Deh-Cho, big river or Inuvialuktun: Kuukpak, great river) is the largest and longest river system in Canada, and is exceeded only by the Mississippi River system in North America. It flows through a vast, isolated region of forest and tundra entirely within the country's Yukon as well as Northwest Territories, although its many tributaries reach into four other Canadian provinces and territories. The river's mainstem runs 1738 km in a northerly direction to the Arctic Ocean, draining a vast area nearly the size of Indonesia. It is the largest river flowing into the Arctic from North America, and with its tributaries is one of the longest rivers in the world.

Course

Rising out of the marshy western end of Great Slave Lake, the Mackenzie River flows generally west-northwest for about 300 km, passing the hamlet of Fort Providence. At Fort Simpson it is joined by the Liard River, its largest tributary, then swings towards the Arctic, paralleling the Franklin Mountains as it receives the North Nahanni River. The Keele River enters from the left about 100 km above Tulita, where the Great Bear River joins the Mackenzie. Just before crossing the Arctic Circle, the river passes Norman Wells, then continues northwest to merge with the Arctic Red and Peel rivers. It finally empties into the Beaufort Sea, part of the Arctic Ocean, through the vast Mackenzie Delta.  

Most of the Mackenzie River is a broad, slow-moving waterway; its elevation drops just 156 m 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 2 to wide and 8 to deep in most parts, and is thus easily navigable except when it freezes over in the winter. However, there are several spots where the river narrows to less than half a kilometre (0.3 mi) and flows quickly, such as at the Sans Sault Rapids at the confluence of the Mountain River and "The Ramparts", a 40 m deep canyon south of Fort Good Hope.  

Watershed

At 1805200 km2, the Mackenzie River's watershed or drainage basin is the largest in Canada, encompassing nearly 20% of the country.  From its farthest headwaters at Thutade Lake in the Omineca Mountains to its mouth, the Mackenzie stretches for 4241 km across western Canada, making it the longest river system in the nation and the thirteenth longest in the world. The river discharges more than 325 km3 of water each year, accounting for roughly 11% of the total river flow into the Arctic Ocean.   The Mackenzie's outflow holds a major role in the local climate above the Arctic Ocean with large amounts of warmer fresh water mixing with the cold seawater. 

Many major watersheds of North America border on the drainage of the Mackenzie River. Much of the western edge of the Mackenzie basin runs along the Continental Divide. The divide separates the Mackenzie watershed from that of the Yukon River and its headstreams the Pelly and Stewart rivers, which flow to the Bering Strait; and the Fraser River and Columbia River systems, both of which run to the Pacific Ocean.  Lowland divides in the north distinguish the Mackenzie basin from those of the Anderson, Horton, Coppermine and Back Rivers – all of which empty into the Arctic. Eastern watersheds bordering on that of the Mackenzie include those of the Thelon and Churchill Rivers, both of which flow into Hudson Bay. On the south, the Mackenzie watershed borders that of the North Saskatchewan River, part of the Nelson River system, which empties into Hudson Bay after draining much of south-central Canada.

Through its many tributaries, the Mackenzie River basin covers portions of five Canadian provinces and territories – British Columbia (BC), Alberta, Saskatchewan, Yukon, and Northwest Territories. The two largest headwaters forks, the Peace and Athabasca Rivers,  drain much of the central Alberta prairie and the Rocky Mountains in northern BC then combine into the Slave River at the Peace-Athabasca Delta near Lake Athabasca, which also receives runoff from northwestern Saskatchewan.  The Slave is the primary feeder of Great Slave Lake (contributing about 77% of the water); other inflows include the Taltson, Lockhart and Hay Rivers, the latter of which also extends into Alberta and BC.  Direct tributaries of the Mackenzie from the west such as the Liard and Peel Rivers carry runoff from the mountains of the eastern Yukon. 

The eastern portion of the Mackenzie basin is dominated by vast reaches of lake-studded boreal forest and includes many of the largest lakes in North America. By both volume and surface area, Great Bear Lake is the biggest in the watershed and third largest on the continent, with a surface area of 31153 km2 and a volume of 2236 km3.  Great Slave Lake is slightly smaller, with an area of 28568 km2 and containing 2088 km3 of water, although it is significantly deeper than Great Bear. The third major lake, Athabasca, is less than a third that size with an area of 7800 km2. Six other lakes in the watershed cover more than 1000 km2, including the Williston Lake reservoir, the second-largest artificial lake in North America, on the Peace River.

With an average annual flow of 9910 m3/s, the Mackenzie River has a smaller discharge than the St Lawrence but is the fourteenth largest in the world in this respect.  About 60% of the water comes from the western half of the basin, which includes the Rocky, Selwyn, and Mackenzie mountain ranges out of which spring major tributaries such as the Peace and Liard Rivers, which contribute 23% and 27% of the total flow, respectively. In contrast the eastern half, despite being dominated by marshland and large lakes, provides only about 25% of the Mackenzie's discharge.  During peak flow in the spring, the difference in discharge between the two halves of the watershed becomes even more marked. While large amounts of snow and glacial melt dramatically drive up water levels in the Mackenzie's western tributaries, large lakes in the eastern basin retard springtime discharges. Breakup of ice jams caused by sudden rises in temperature – a phenomenon especially pronounced on the Mackenzie – further exacerbate flood peaks. In full flood, the Peace River can carry so much water that it inundates its delta and backs upstream into Lake Athabasca, and the excess water can only flow out after the Peace has receded. 

Geology

As recently as the end of the last glacial period eleven thousand years ago the majority of northern Canada was buried under the enormous continental Laurentide ice sheet. The tremendous erosive powers of the Laurentide and its predecessors, at maximum extent, completely buried the Mackenzie River valley under thousands of meters of ice and flattened the eastern portions of the Mackenzie watershed. When the ice sheet receded for the last time, it left a 1100 km-long postglacial lake called Lake McConnell, of which Great Bear, Great Slave and Athabasca Lakes are remnants.  Significant evidence exists that roughly 13,000 years ago, the channel of the Mackenzie was scoured by one or more massive glacial lake outburst floods unleashed from Lake Agassiz, formed by melting ice west of the present-day Great Lakes. At its peak, Agassiz had a greater volume than all present-day freshwater lakes combined.  This is believed to have disrupted currents in the Arctic Ocean and led to an abrupt 1,300-year-long cold temperature shift called the Younger Dryas. 

Ecology

The Mackenzie River's watershed is considered one of the largest and most intact ecosystems in North America, especially in the north. Approximately 63% of the basin – 1137000 km2 – is covered by forest, mostly boreal, and wetlands comprise some 18% of the watershed – about 324900 km2. More than 93% of the wooded areas in the watershed are virgin forest. There are fifty-three fish species in the basin, none of them endemic.  Most of the aquatic species in the Mackenzie River are descendants of those of the Mississippi River and its tributaries. This anomaly is believed to have been caused by hydrologic connection of the two river systems during the Ice Ages by meltwater lakes and channels. 

Fish in the Mackenzie River proper include the northern pike, some minnows, and lake whitefish, and the river's shores are lined with sparse vegetation like dwarf birch and willows, as well as numerous peat bogs. Further south the tundra vegetation transitions to black spruce, aspen and poplar forest. Overall, the northern watershed is not very diverse ecologically, due to its cold climate – permafrost underlies about three-quarters of the watershed, reaching up to 100 m deep in the delta region – and meager to moderate rainfall, amounting to about 410 mm over the basin as a whole.  The southern half of the basin, in contrast, includes larger reaches of temperate and alpine forests as well as fertile floodplain and riparian habitat, but is actually home to fewer fish species due to large rapids on the Slave River preventing upstream migration of aquatic species. 

Migratory birds use the two major deltas in the Mackenzie River basin – the Mackenzie Delta and the inland Peace-Athabasca Delta – as important resting and breeding areas. The latter is located at the convergence of four major North American migratory routes, or flyways.  As recently as the mid-twentieth century, more than 400,000 birds passed through during the spring and up to a million in autumn. Some 215 bird species in total have been catalogued in the delta, including endangered species such as the whooping crane, peregrine falcon and bald eagle. The construction of the W.A.C. Bennett Dam on the Peace River has reduced the seasonal variations of water levels in the delta, causing damage to its ecosystems. Populations of migratory birds in the area have steadily declined since the 1960s. 

History

The Mackenzie (previously Disappointment) River was named after Scottish explorer Alexander Mackenzie, who travelled the river in the hope it would lead to the Pacific Ocean, but instead reached its mouth on the Arctic Ocean on 14 July 1789. No European reached its mouth again until Sir John Franklin on 16 August 1825. The following year he traced the coast west until blocked by ice while John Richardson followed the coast east to the Coppermine River. In 1849 William Pullen reached the Mackenzie from Bering Strait.

The Royal Canadian Mint honoured the 200th anniversary of the naming of the Mackenzie River with the issue of a silver commemorative dollar in 1989.

In 1997, a cultural landscape along the section of the Mackenzie River at Tsiigehtchic was designated the Nagwichoonjik (Mackenzie River) National Historic Site of Canada due to its cultural, social and spiritual significance to the Gwichya Gwich'in. 

In 2008, Canadian and Japanese researchers extracted a constant stream of natural gas from a test project at the Mallik methane hydrate field in the Mackenzie Delta. This was the second such drilling at Mallik: the first took place in 2002 and used heat to release methane. In the 2008 experiment, researchers were able to extract gas by lowering the pressure, without heating, requiring significantly less energy.  The Mallik gas hydrate field was first discovered by Imperial Oil in 1971–1972. 

Human use

As of 2001, approximately 397,000 people lived in the Mackenzie River basin – representing only 1% of Canada's population. Ninety percent of these people lived in the Peace and Athabasca River drainage areas, and mainly in Alberta. The cold northern permafrost regions beyond the Arctic Circle are very sparsely populated, mainly by indigenous peoples. As a result, much of the Mackenzie watershed consists of unbroken wilderness and human activities presently have little influence on water quality or quantity in the basin's major rivers.  Perhaps the heaviest use of the watershed is in resource extraction – oil and gas in central Alberta, lumber in the Peace River headwaters, uranium in Saskatchewan, gold in the Great Slave Lake area and tungsten in the Yukon. Especially in the case of oil, these activities are beginning to pose a threat to riverine ecology in the headwaters of the Mackenzie River. 

During the ice-free season, the Mackenzie is a major transportation link through the vast wilderness of northern Canada, linking the numerous scattered and isolated communities along its course. Canada's northernmost major railhead is located at the town of Hay River, on the south shore of Great Slave Lake. Goods shipped there by train and truck are loaded onto barges of the Inuit-owned Northern Transportation Company.  Barge traffic travels the entire length of the Mackenzie in long "trains" of up to fifteen vessels pulled by tugboats, with the sole exception being in a few of the river's narrows, where the barges are uncoupled and towed one by one through difficult stretches. Goods are shipped as far as the town of Tuktoyaktuk on the eastern end of the Mackenzie Delta. From there they are further distributed among communities along Canada's Arctic coast and the numerous islands north of it.  During the winter, the frozen channel of the Mackenzie River, especially in the delta region, is crisscrossed with ice roads served by dogsleds and snowmobiles. 

Although the entire main stem of the Mackenzie River is undammed, many of its tributaries and headwaters have been developed for hydroelectricity production, flood control and agricultural purposes. The W.A.C. Bennett Dam and Peace Canyon Dam on the upper Peace River were completed in 1968 and 1980 for power generation purposes. The two dams, both owned by BC Hydro, have a combined capacity of more than 3,400 megawatts (MW).   The reservoir of W.A.C. Bennett – Williston Lake – is the largest body of fresh water in BC and the ninth largest man-made lake in the world, with a volume of .  Williston's additional purpose of flood control has led to reduced flooding in the Peace River valley, the Peace-Athabasca Delta, and the Slave River, which while providing for better farming conditions, has had significant impacts on wildlife and riparian communities. The decrease in annual flow fluctuations has had impacts as far downstream as the main stem of the Mackenzie.  

Agriculture in the Mackenzie River basin is mainly concentrated in the southern portion of the watershed, namely the valleys of the Peace and Athabasca Rivers. The valley of the former river is considered to be some of the best northern farmland in Canada. These conditions are expected to be improved even more by recent trends in climate change, such as warmer temperatures and a longer growing season.   It is even said that "there is enough agricultural capability in the Peace River Valley to provide vegetables to all of northern Canada".  However, reaches of the Peace River Valley are threatened with flooding by the proposed Site C Dam, which would generate enough electricity to power about 460,000 households. Site C has been the center of a protracted and ongoing environmental battle since the 1970s, and a decision has not yet been reached as to whether or not to build the dam. 

Site C is not the only proposed water project in the Mackenzie basin. A potential US$1 billion run-of-the-river hydroelectricity station on the Slave River would generate at least 1,350 MW of power.   Some tentative proposals have gone as far as to include dams on the main stem of the Mackenzie itself.  By far the largest engineering project ever slated for the Mackenzie River was the North American Water and Power Alliance (NAWAPA), a vast series of dams, tunnels and reservoirs designed to move 150 km3 of Arctic meltwater to southern Canada, the western United States and Mexico. The system would involve building massive dams on the Liard, Mackenzie, Peace, Columbia, and Fraser rivers, then pumping water into a 650 km long reservoir in the Rocky Mountain Trench. The water would then flow by gravity to irrigate more than 220000 km2 in the three countries and generate more than 50,000 MW of surplus energy.  First proposed in the 1950s, the project's estimated cost has since risen to over $200 billion. Because of its massive cost and environmental impacts, it is considered unlikely ever to be implemented. 

Tributaries

Largest

Full list
Deh Cho River Mackenzie River Delta Mackenzie River Valley Mackenzie river River Mackenzie Disappointment River MacKenzie River Mackenzie valley Mackenzie River delta Mackenzie River, Northwest Territories Mackenzie Valley Mackenzie River
river mackenzie deh cho river mackenzie river delta mackenzie river mackenzie river valley mackenzie valley mackenzie river northwest territories disappointment river
mackenzie river
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Mackenzie River
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