Meghan Hodges
Lake Ontario is the last of the Great Lakes that straddle the Canada-US border and is the smallest of the Great Lakes. It has been polluted for at least a few decades, with pollution coming from farms, businesses, urban industrial centers, and the other Great Lakes that flow into it. The human population in the Lake Ontario basin has increased by more than 60% over the past 50 years, which has impacted the lake. While the lake is generally safe for swimming and fishing, there are localized impaired zones, and the beaches are often polluted with plastic.
| Characteristics | Values |
|---|---|
| Pollution Sources | Urban industrial centers (Hamilton and Toronto), farms, businesses, stormwater, sewage, and garbage |
| Pollutants | Plastics, Cladophora, phosphorus, chloride, naphthalene, and other volatile compounds |
| Impact on Wildlife | Fish with tumors and reproductive deformities, destroyed habitats, altered food webs |
| Human Impact | Swimming restrictions, consumption advisories for certain fish species, water quality issues |
| Remedial Actions | Cleanup efforts, invasive species control, wetland restoration, contaminated zone containment |
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What You'll Learn
Lake Ontario is the most polluted of the Great Lakes
Lake Ontario is the most downstream of the Great Lakes, which means that it is impacted by human activities in the basins of the other Great Lakes—Lake Superior, Michigan, Huron, and Erie. All of the other lakes flow into it, giving it their pollution. It also receives runoff from farms and businesses around it.
The human population in the Lake Ontario basin has increased by more than 60% over the past 50 years, which is the highest of all the Great Lakes basins. Urban industrial centers like Hamilton and Toronto on the Canadian side have contributed to the lake's pollution. In 1985, Hamilton Harbour was identified as an area of concern under the Canada-U.S. Great Lakes Water Quality Agreement due to industrial pollution from the area's steelmaking facilities. A $139 million underwater box is being built to contain an underwater contaminated zone in Hamilton's Randle Reef.
Invasive species, including sea lamprey, mussels, and Phragmites, have significantly altered habitats and the food web in Lake Ontario. Groundwater quality is assessed as fair with elevated chloride levels due to road salt being an issue. Coastal wetlands have been impacted by development, past water level regulation, and invasive species. However, coastal wetland amphibians and birds are showing improving trends.
The percentage of days during the swimming season that Lake Ontario's monitored beaches are open and safe for swimming has increased over the past ten years. The current status of harmful algal blooms in the lake is good with an unchanging trend, although there are localized impaired zones in some embayments. Toxic chemicals monitored in the lake are assessed as fair, and long-term trends indicate that concentrations are declining, including declines in contaminant concentrations in fish filets. Lake Ontario fish continue to be a nutritious food source, although consumption advisories for certain species remain in effect.
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Human activity and urbanisation
Lake Ontario is the last of the Great Lakes that straddle the Canada-US border and is impacted by human activities across the Lake Superior, Michigan, Huron, and Erie basins. As the downstream Great Lake, it receives runoff from farms and businesses around it, as well as the other lakes. The human population in the Lake Ontario basin has increased by more than 60% in the past 50 years, the highest of all the Great Lakes basins.
The lake's water quality has been affected by industrial pollution from steelmaking facilities in Hamilton Harbour, which was identified as an area of concern in 1985. A $139 million underwater box is being built to contain a 150-year-old contaminated zone in Hamilton's Randle Reef. The lake has also been impacted by the rapid urban population growth on the Canadian side of the basin, with Toronto and Hamilton being major urban industrial centres.
Invasive species, such as sea lamprey, mussels, and Phragmites, have significantly altered the habitat and food web in Lake Ontario. These species have impacted coastal wetlands, along with past water level regulation. However, coastal wetland amphibians and birds are showing improving trends. The lake's groundwater quality is assessed as fair, with elevated chloride levels due to road salt being an issue.
The percentage of days during the swimming season that Lake Ontario's monitored beaches are open and safe for swimming has increased over the past ten years. While the lake's water quality is generally considered fair, there are localized impaired zones in some embayments. The current status of harmful algal blooms is good with an unchanging trend. Consumption advisories for certain species of fish remain in effect, but some have become less restrictive due to clean-up efforts.
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Industrial pollution
Lake Ontario, the easternmost, lowest in elevation, and smallest in surface area of the Great Lakes, has been subjected to industrial pollution for over a century. The lake, which forms part of the border between Canada and the United States, has been impacted by human activities, including pollution from industrial centres such as Hamilton and Toronto on the Canadian side.
The industrial revolution and the subsequent economic development in the region led to a significant decline in the water quality of the Great Lakes, including Lake Ontario. The lakes became polluted with unwanted species and industrial, agricultural, and urban waste. This pollution was exacerbated by the lack of substantial government oversight in the Great Lakes Basin, allowing waste, pesticides, and fertilizers from surrounding cities, industrial plants, and agriculture to contaminate the lake.
In 1948, the US government passed the Federal Water Pollution Act to address water contamination. The formation of the IJC Lakes Superior-Huron-Erie Advisory Board and the Lakes Erie-Ontario Advisory Board in 1946 and 1948 further demonstrated efforts to tackle the issue. These boards focused on monitoring and addressing industrial and chemical pollution in the Great Lakes region.
Despite these efforts, Lake Ontario continues to face industrial pollution challenges. Hamilton Harbour, for example, was identified as an area of concern in 1985 due to industrial pollution from the area's steelmaking facilities. A plan to contain the contaminated zone in Hamilton's Randle Reef with an underwater box is currently underway. The lake also receives agricultural runoff, urban waste discharges, and industrial waste from within its own basin.
The human population in the Lake Ontario basin has increased by more than 60% in the past 50 years, impacting the lake's health. However, there are some positive signs, such as the improving health of coastal wetlands and the increasing number of days during the swimming season when the lake's beaches are safe for swimming.
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Stormwater and sewage
Lake Ontario has been subject to pollution from stormwater and sewage for over a century. The Industrial Revolution and the emergence of new economic activities and cultural centres in the region led to pollution from industry, agriculture, and cities. This resulted in the contamination of the Great Lakes' connecting channels, rivers, and Lake St. Clair, as observed in a 1946-1950 transboundary pollution study.
In the past, Toronto's sewage system pumped raw sewage into Lake Ontario, contributing to the pollution issue. The lake has also received insufficiently treated urban stormwater, which introduces unwanted phosphorus and contaminants. While the province has invested significantly in wastewater and stormwater infrastructure projects, the problem persists.
The Ontario Water Resources Act and Environmental Protection Act were established to manage the water quality impacts of municipal and industrial sewage and stormwater through permit and approval systems. Additionally, Ontario introduced permits to manage large water extractions and protect water quantity. The province has also supported local water and wastewater infrastructure by committing grants and loans.
To address the issue of stormwater, a review completed in 2010 emphasized the importance of "green infrastructure" or low-impact development, such as constructed wetlands, combined with conventional stormwater systems. This helps communities adapt to the impacts of climate change and reduces sewage overflows. Ontario has also initiated outreach and guidance on integrated stormwater practices.
While Lake Ontario continues to face challenges with stormwater and sewage pollution, efforts are being made to improve the situation. The degree of pollution in the lake has been a contentious issue, with some arguing that it is safe to swim in most of the time, except after heavy rains when the sewage plants might overflow.
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Invasive species
The condition of Lake Ontario has been fluctuating since European settlement, with changes in the physical and chemical environment of the lake due to non-indigenous species, pollution, sedimentation, turbidity, and climate change.
The Central Lake Ontario Conservation Authority (CLOCA) has implemented an Invasive Species Management Strategy to address the issue. This strategy includes education and outreach initiatives, as well as species-specific management plans and clean equipment protocols. CLOCA actively engages with municipal staff and environmental non-governmental organizations (ENGOs) to collaborate on projects and workshops related to invasive species management.
In addition to the zebra and quagga mussels, other invasive species such as Phragmites and Hybrid Cattail have impacted the coastal wetlands of Lake Ontario. The introduction of invasive species, along with other stressors like development, dams, non-point source pollution, and climate change, has led to habitat degradation and loss in the lake's ecosystem.
The Great Lakes Restoration Initiative (GLRI) in the US and the Canada-Ontario Agreement have also played a role in protecting and restoring the Great Lakes, including Lake Ontario. These efforts have resulted in the clean-up of polluted harbours and the restoration of habitats for fish and wildlife.
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Frequently asked questions
Yes, Lake Ontario is polluted. It is impacted by human activities in the Lake Superior, Michigan, Huron, and Erie basins.
Lake Ontario is affected by pollution from the other Great Lakes, as well as runoff from farms and businesses. Additionally, it faces issues such as nutrient loading, invasive species, and the impact of coastal development.
Lake Ontario has likely been polluted for over a century due to industrial activities and the disposal of wastewater and industrial waste.
The pollution has led to contaminated water, declines in fish populations, and the destruction of habitats. However, long-term trends indicate that contaminant concentrations are declining, and the lake continues to be a source of drinking water and nutritious fish.
Efforts are being made to improve the situation, such as clean-up initiatives and the construction of an underwater box to contain contaminated zones. Coastal wetland amphibians and birds are also showing improving trends.
