Lake Ontario's Pollution Problem: A Troubled Waterway

Lake Ontario, the easternmost of the Great Lakes, is considered to have a fair ecosystem, with some improvements but also persistent issues. The lake receives agricultural runoff and urban and industrial waste discharges, and its beaches and nearshore waters are impacted by excessive growth of Cladophora, an invasive species, due in part to nutrient loading and increased water clarity caused by the filtering effects of invasive mussels. The lake's groundwater quality is assessed as fair due to elevated chloride levels from road salt, and it faces additional stressors from rapid urban population growth on its Canadian side. While the drinking water supply is generally safe, toxic chemicals such as polycyclic aromatic hydrocarbons have been found in the lake, and invasive species continue to alter the habitat and food web. However, there are also signs of improvement, with declining contaminant concentrations in fish and increasing populations of native prey fish and lake sturgeon.

Lake Ontario's ecosystem health is considered 'fair'

Lake Ontario's ecosystem health is considered "fair", with some improvements but also persistent issues. The lake, which is bordered on the south by New York and on the north by the province of Ontario, has seen a decrease in beach closings and contaminant concentrations in fish. However, it faces challenges such as invasive species, nutrient loading, and the impact of climate change.

The lake's beaches and nearshore waters provide good opportunities for swimming and other recreational activities. Over the past decade, the percentage of days during the swimming season that monitored beaches are open and safe for swimming has increased. This is due to the improving quality of the lake's water, which has been rated as "fair" to "good" in recent years.

However, one of the main concerns for Lake Ontario is the presence of invasive species. Dreissenid mussels, commonly known as zebra and quagga mussels, are increasing in deep zones and could disrupt the delicate food webs in the water. Additionally, the development of invasive plant life, such as typha cattails, has been rated as "poor". These invasive species have significantly altered the habitat and food web within the lake.

Another issue impacting the lake is nutrient loading, particularly excessive growth of Cladophora in some nearshore areas. This is due in part to increased water clarity caused by the filtering effects of invasive mussels, as well as nutrient runoff from agriculture, and urban and industrial waste discharges within its own basin. While the current status of harmful algal blooms is considered "good", there are localized impaired zones in some embayments.

Groundwater quality in the lake is assessed as "fair", with elevated chloride levels due to road salt being an issue. Land-based stressors, such as rapid urban population growth, also continue to impact the lake. Despite these challenges, there are signs of improvement in the lake's ecosystem. Coastal wetland amphibians and birds are showing improving trends, and habitat connectivity between the tributaries and the lake is rated as "fair" with an improving trend. Lake Trout populations are also improving due to successful Sea Lamprey control, and native prey fish populations are recovering naturally or through restoration efforts.

Industrial pollution and contaminated sites

Lake Ontario, the easternmost, lowest in elevation, and smallest Great Lake, is bordered on the south by New York and on the north by the province of Ontario. The lake's ecosystem health is considered "fair," with some improvements and persistent concerns. One of the key issues impacting the lake is industrial pollution, which has resulted in contaminated sites and affected the water quality.

Industrial activities, particularly in the Hamilton Harbour area, have contributed to the contamination of Lake Ontario. Randle Reef, located in Hamilton Harbour, has been identified as one of the "areas of concern" for pollution in the Great Lakes. The site is contaminated with coal tar, a by-product of coal gasification, and other toxic substances such as polycyclic aromatic hydrocarbons and heavy metals. The contamination has been releasing contaminants into the lake for decades, impacting the underwater ecosystem and the health of the surrounding area.

To address the pollution at Randle Reef, a $139 million underwater containment structure is being built to enclose and contain the contaminated sediment. This project aims to mitigate the spread of contamination and improve the water quality in the area. However, critics argue that simply containing the pollution without addressing the root causes may not be a sustainable solution.

In addition to industrial pollution, Lake Ontario also faces challenges from agricultural runoff, urban population growth, and invasive species. These factors contribute to nutrient loading, increased water clarity, and disruptions to the natural food web. Despite these issues, there have been some improvements in water quality, with a decrease in contaminant concentrations in fish and fewer beach closures.

Overall, while Lake Ontario faces significant challenges due to industrial pollution and contaminated sites, there are ongoing efforts to address these issues and improve the ecosystem health of the lake. The cooperation between the U.S. Environmental Protection Agency and Environment and Climate Change Canada is a positive step towards restoring and protecting this important shared environmental resource.

Invasive species and wetland habitat loss

Lake Ontario, the easternmost, lowest in elevation, and smallest in surface area of the Great Lakes, is also perhaps the most polluted. As the last lake in the chain, Ontario receives the accumulation of contaminants from the other Great Lakes, in addition to agricultural runoff and urban and industrial waste discharges within its own basin.

The lake's ecosystem health has been rated as "fair," with some progress being made, but persistent concerns, such as invasive species and wetland habitat loss, remain.

Invasive species, including sea lamprey, invasive mussels (zebra and quagga mussels), and Phragmites, have significantly altered the habitat and food web within the lake. The development of invasive plant life in wetlands, such as Typha cattails, has been rated as "poor" in Lake Ontario. These invasive species have disrupted the delicate food webs in the water, and wetlands that once boasted diverse ecological mosaics have lost much of their diversity.

Coastal wetlands have been impacted by development, past water level regulation, and invasive species. However, there are signs of improvement, with coastal wetland amphibians and birds showing improving trends. Habitat connectivity between the tributaries and the lake is rated as "fair" and improving. Additionally, lake trout populations are improving due to successful sea lamprey control, and some native prey fish populations are recovering naturally or through successful restoration efforts.

Groundwater quality and elevated chloride levels

The groundwater quality of Lake Ontario is assessed as "Fair" with some concerns about elevated chloride levels. The primary cause of these elevated levels is the use of road salts, which are used for winter safety. Urban stormwater and runoff from roads containing salt are also potential causes of adverse effects in urban rivers. The Ontario Ministry of the Environment, Conservation and Parks monitors chloride levels at over 2,500 surface and groundwater sampling locations across the province, some of which date back to the 1960s.

While most historical chloride data indicate concentrations are below the Canadian Water Quality Guideline, many lake, stream, and groundwater sampling locations near roadways or in urban areas meet or exceed this guideline. These concentrations are also persistently increasing. The impact of road salting activities on water quality is particularly notable in intensely urban areas, where chloride levels in Lake Ontario are highest.

The ministry has also identified the linkages between precipitation and other parts of the hydrologic cycle, collecting measurements like soil moisture, groundwater levels, and stream flow. This data will help build an integrated surface-groundwater model that can simulate the hydrologic cycle. Climate change may also play a role in rising chloride levels, as years with more precipitation and greater snow depth in the winter tend to have higher chloride concentrations.

In addition to road salt and climate factors, land use changes can also influence water quality. For example, in the 1960s and 1970s, phosphorus levels in Lake Ontario were elevated due to excess phosphorus loading from multiple land use activities. This excess phosphorus contributed to the growth of planktonic algae and harmful algal blooms. While phosphorus levels are now considered fair, the impact of land use changes on water quality is an ongoing concern.

Agricultural runoff and urban waste

Lake Ontario is bordered on the south by New York and on the north by the Canadian province of Ontario. The lake empties into the St. Lawrence River, which eventually reaches the Atlantic Ocean. As the heartland of Canada's commercial, industrial, and population centres, the lake is vulnerable to agricultural runoff and urban waste.

Agricultural runoff from farms and manure has been a significant issue for the Great Lakes, including Lake Ontario. A binational report by American and Canadian experts concluded that voluntary measures to mitigate farm manure pollution have been ineffective. It recommended that governments implement laws to protect the lakes from runoff. This is particularly important for Lake Erie, where uncontrolled algae growth fuelled by phosphorus in animal waste has created dead zones.

The International Joint Commission's draft report highlights the need for regulatory protections in domestic action plans to address the issue. It aims to reduce phosphorus runoff from Lake Erie by 40%. While phosphorus limits in detergents and sewage treatment improvements were effective in the 1970s, the problem has worsened in the western Lake Erie basin despite non-mandatory abatement efforts.

Additionally, urban waste and development have impacted Lake Ontario's coastal wetlands. The human population in the Lake Ontario basin has increased by over 60% in the past 50 years, the highest growth among all the Great Lakes basins. This rapid urban expansion has contributed to the lake's land-based stressors. Furthermore, industrial pollution has severely affected Lake Ontario, with Randle Reef in Hamilton Harbour being listed as one of 43 "areas of concern" for pollution in the Great Lakes.

To address the pollution at Randle Reef, a $139 million underwater box is being constructed to contain the contaminated zone for approximately 200 years. While this solution has faced criticism, it highlights the need for urgent action to address the legacy of industrial contamination in Lake Ontario and other Canadian waters.

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