Meghan Hodges
Great Slave Lake, located in Canada's Northwest Territories, is a pristine and massive lake that is the deepest in North America. It is a popular destination for anglers and tourists alike, with its clear and deep waters providing a picturesque setting for various recreational activities. However, despite its natural beauty, the lake has faced environmental challenges due to human activities, particularly mining, which has introduced contaminants affecting water quality. While the lake is generally rich in aquatic life, residents of Yellowknife cannot drink its water due to pollution concerns. This raises the question: Is Great Slave Lake polluted?
| Characteristics | Values |
|---|---|
| Pollution | The lake is considered to be pristine and unspoiled, with clean water and a general absence of pollution. However, there is some contamination from mining activities, including arsenic trioxide waste, which has impacted the water quality, making it unsuitable for drinking. |
| Water Quality | The GNWT monitors water quality, and in 2020, higher concentrations of metals and hydrocarbons were detected due to increased suspended sediment from heavy rains and runoff. |
| Fish Stocks | The lake is rich in aquatic life, with various fish species such as northern pike, lake whitefish, lake trout, inconnu, walleye, and more. However, commercial production has strained fish stocks, and some species are still recovering. |
| Climate | The lake is located in a sub-Arctic region and is at least partially frozen for about eight months of the year. It experiences all four seasons, with stormy weather becoming more common in the fall. |
| Geography | Great Slave Lake is the second-largest lake in the Northwest Territories, Canada, and the deepest lake in North America at 614 meters. It has an irregular shoreline and is surrounded by forests, tundra, and the Canadian Shield. |
| History | The lake has a rich history, with archaeological evidence of Indigenous settlements dating back thousands of years. It was put on European maps during the fur trade in the mid-18th century and has since been a hub for gold mining and commercial fishing. |
| Ecology | The lake is home to diverse flora and fauna, including woodland caribou, moose, and various bird species. It is also a breeding ground for shorebirds, songbirds, and waterfowl. |
| Population | The lake's surrounding area is home to a small population of less than 20,000 people, with the largest community being Yellowknife. |
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What You'll Learn
Arsenic trioxide waste from the Giant Mine
Great Slave Lake, located in Canada's Northwest Territories, is the second-largest lake entirely within Canadian borders, the deepest lake in North America, and the tenth-largest lake in the world. The lake is perceived as one of the most pristine water bodies globally, but residents of Yellowknife, on its northern shore, cannot drink its water and must draw their water supply from the Yellowknife River, situated five kilometres away.
The lake's water has been polluted by the mining industry, and the biggest single source of pollution is arsenic trioxide waste from the Giant Mine. Arsenic trioxide is a toxic form of arsenic created during the mining process. During the life of the mine, arsenic tailings spilled into Back Bay, contaminating the water supply for the mine and the city of Yellowknife, as well as surrounding communities.
The roasting process used to extract gold from arsenopyrite rock released arsenic trioxide and sulfur dioxide into the air. Pollution control devices installed during the 1950s captured arsenic dust, but contamination was still detected in the 1970s. Roasting was discontinued in 1999, but around 237,000 to 238,000 tons of highly toxic arsenic trioxide dust were stored in 14 to 15 underground chambers a few hundred meters from Great Slave Lake. The chambers are surrounded by solid rock and sealed with concrete bulkheads, but there are concerns about arsenic leaching into the groundwater.
Freezing the arsenic trioxide waste in place has been determined to be the best strategy for long-term management, but it is not a permanent solution. The Giant Mine Remediation Project (GMRP) is working to ensure that remediation activities do not negatively impact the health of nearby communities. Arsenic level monitoring in the communities will continue, with retesting of children scheduled for 2023 and adults in 2027-2028.
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Pollution from local mining activities
Great Slave Lake is a pristine lake in Canada's Northwest Territories. It is the deepest lake in North America, reaching a maximum depth of 614-615 metres. The lake is a remnant of the vast glacial Lake McConnell and is fed by the Slave River, which provides the lake with high nutrient levels.
Despite its reputation as one of the most pristine lake environments in the world, the lake has faced pollution from local mining activities. The biggest single source of pollution is arsenic trioxide waste generated by the Giant Mine. During the life of the mine, arsenic tailings spilled into Back Bay, contaminating the water supply for the mine, the city of Yellowknife, and surrounding communities. The roasting process used to extract gold from arsenopyrite rock released arsenic trioxide and sulfur dioxide into the air, and while pollution control processes were eventually added, contamination continued.
The Canadian government and mine owners are working to evaluate strategies for managing arsenic trioxide waste and protecting the environment. However, concerns remain about the potential leaching of arsenic into groundwater. In addition to arsenic contamination, snowmelt and heavy rain in 2020 resulted in higher-than-normal concentrations of some metals and hydrocarbons in the lake. Long-term monitoring of water quality will help detect changes and protect this valuable ecosystem.
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Long-range contaminants in lake-bed sediments, fish, and other aquatic species
Great Slave Lake is perceived as one of the most pristine water bodies in the world. However, long-range contaminants have been found in lake-bed sediments, fish, and other aquatic species.
The biggest single source of pollution is arsenic trioxide waste generated by the Giant Mine. During the life of the mine, arsenic tailings spilled into Back Bay, contaminating the water supply for the mine and the city of Yellowknife, as well as for surrounding communities. Beginning in 1943, the "roasting" process used to remove gold from arsenopyrite rock sent arsenic trioxide and sulfur dioxide into the air. Although pollution control devices were installed in the 1950s, contamination was still detected in the 1970s. Roasting was discontinued in 1999, but approximately 238,000 tons of highly toxic, water-soluble arsenic trioxide dust are currently stored in underground chambers close to the lake. There are concerns about arsenic leaching into the groundwater. The Canadian government and mine owners are working to evaluate strategies for managing waste and protecting the environment.
In addition to arsenic, other substances have been found in the lake at higher-than-normal concentrations. For example, snowmelt and heavy rain in 2020 resulted in increased suspended sediment (dirt, silt, and clay) in the lake, which in turn caused higher concentrations of some metals and hydrocarbons. These substances are not believed to affect the health of bugs and fish.
The lake is also affected by climate change, specifically reduced ice coverage times, which impacts aquatic life.
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Unsuitable for drinking due to historical human activity
Great Slave Lake, located in Canada's Northwest Territories, is the deepest lake in North America. It is perceived as one of the most pristine water bodies in the world. However, the lake's water is unsuitable for drinking due to historical human activity, particularly mining, which has introduced contaminants affecting water quality.
Mining activities in the region have resulted in pollution from arsenic trioxide waste, which has contaminated the water supply for nearby communities. Beginning in the 1940s, gold was extracted from ore through a process called roasting, which released arsenic trioxide and sulfur dioxide into the air. While pollution control devices were eventually implemented, contamination continued, and roasting was only discontinued in 1999. As a result, a significant amount of highly toxic arsenic trioxide dust is now stored in underground chambers close to the lake, raising concerns about potential leaching into the groundwater.
In addition to arsenic contamination, the lake has also been impacted by other human activities. For example, the federal government's scientific oversight and commercial production strained the fish stocks in the lake. While some species have recovered, others have faced more complex challenges. Furthermore, climate change, specifically reduced ice coverage, is impacting the populations of various fish species in the lake.
The effects of human activity on the lake's water quality are significant enough to render it unsuitable for drinking. Residents of Yellowknife, on the northern shore, must rely on water from the Yellowknife River, located several kilometres away. The Canadian government and mine owners are working to address the environmental impact of mining activities and manage the arsenic waste effectively.
While Great Slave Lake faces challenges due to historical human activity, it remains a vital and celebrated natural landmark, integral to the Mackenzie River watershed and home to a diverse range of flora and fauna.
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Climate change and reduced ice coverage times impacting aquatic life
The Great Slave Lake, located in Canada's Northwest Territories, is the second-largest lake in the region, the deepest lake in North America, and the tenth-largest lake globally. The lake is known for its pristine waters and natural beauty, but it has also faced environmental challenges due to human activities and climate change.
Climate change, specifically reduced ice coverage times, is impacting the lake's aquatic life. The lake is at least partially frozen for about eight months of the year, with ice remaining from late November to mid-to-late May. However, the effects of global warming have led to a reduction in ice coverage. This has consequences for the lake's fish populations, including lake whitefish, lake trout, inconnu, northern pike, and walleye. The lake whitefish, in particular, enjoy the highest population levels. The reduced ice coverage can impact the survival of certain fish species, such as the arctic grayling, which can survive under thick ice for up to eight months by consuming aquatic insects, snails, small fish, and fish eggs.
The changing climate also affects the lake's biome. The lake lies south of the treeline, within the northern boreal forest, and experiences a longer growing season due to its moderating influence on the local climate. The average temperature increases in Arctic areas due to climate change are occurring at a faster rate than the worldwide averages, altering the biological structure of the lake's ecosystem. This, in turn, impacts the diverse flora and fauna found in the region, including woodland caribou, moose, and various bird species.
Additionally, the lake's water quality has been affected by human activities, particularly mining. Contamination from mining activities has been detected in the lake's sediments, fish, and other aquatic species. The release of arsenic trioxide and sulfur dioxide during the gold extraction process has been a significant source of pollution, with concerns about the potential leaching of arsenic into groundwater. While pollution control measures have been implemented, the effects of historical contamination continue to be a challenge for the lake's ecosystem.
The Great Slave Lake is a vital habitat for numerous species and a popular destination for fishing and tourism. However, the combined impacts of climate change and human activities have led to reduced ice coverage and water quality issues, highlighting the delicate balance between human activities and the preservation of this pristine natural environment.
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Frequently asked questions
Great Slave Lake is considered one of the most pristine water bodies in the world. However, it has been contaminated by the mining industry.
Arsenic trioxide waste is the biggest single source of pollution in the lake. This was generated by the Giant Mine, and 237,000 tonnes of it is stored in underground chambers.
Arsenic tailings have spilled into Back Bay, contaminating the water supply for Yellowknife and surrounding communities.
Snowmelt and heavy rain in 2020 caused higher concentrations of some metals and hydrocarbons in the lake.
