St. Clair River: Area of Concern

The St. Clair River was designated a binational Area of Concern (AOC) in 1987 under the Canada-U.S. Great Lakes Water Quality Agreement. Years of industrialization, urbanization and agricultural land use activities led to severely degraded water quality and ecosystem health in the river and its tributary watersheds. Nine out of 14 beneficial use impairments (BUIs) were identified, which measure the environmental, human health or economic impact of poor water quality. A further three beneficial uses were deemed as “requiring further assessment”, meaning more information was required to determine whether they were impaired.


Over the past 30 years, there has been significant progress in restoring the water and environmental quality of the river. These include:

  • a 75% reduction in contaminant loads to the river since the introduction of the Municipal Industrial Strategy for Abatement Program to control toxic contaminants in the petroleum and chemical industries
  • the clean-up of 13,300 cubic meters of mercury-contaminated sediment by Dow Chemical in 2002
  • a reduction in bacteria and discharges impacting local beaches and the river, following municipal infrastructure upgrades

Restoration of beneficial uses 

Over the last decade, significant progress has been made to improve environmental conditions on the Canadian side. These beneficial uses are no longer considered “impaired”:

  • tainted fish and wildlife flavour (2011)
  • added costs to agriculture or industry (2012)
  • degradation of aesthetics (visual appearance) (2016)
  • beach closings (2018)
  • restrictions on dredging activities (2018)
  • bird or animal deformities or reproductive problems (2018)

Work continues on restoring the remaining beneficial uses:

  • restrictions on drinking water, taste or odour problems – the frequency of spills has declined since the 1980s and water quality monitoring data is being used to assess the status of this BUI
  • fish and wildlife habitat loss – monitoring data confirms that six of the seven restoration criteria for this BUI have been met, and science is underway to assess the status of this BUI
  • fish and wildlife consumption restrictions – fish contaminant monitoring data shows improvements and wildlife studies show a large decline in concentrations of several contaminants
  • degradation of benthos (organisms that live in and on the bottom of the river) – conditions have improved but sediment remediation is needed to fully address the impact of contaminants on benthos 
  • degradation of fish and wildlife populations – several studies show that fish and wildlife populations within the AOC are similar to or better than populations found outside the AOC
  • fish tumours or other deformities – local and lakewide fish tumour data was assessed and revealed no indication of impairment in the AOC. Agencies are proceeding with next steps to change the status of this BUI from 'requires further assessment' to 'not impaired' 

Recent actions

The overall health of the St. Clair River has improved through these recent actions:

Wastewater management:

  • investment in 2015 for upgrades to the City of Sarnia’s wastewater system, with improvements to pumping stations, wastewater treatment plants and the sewer system, at a cost of $30 million
  • the separation of approximately 15 kilometers of combined sewers in Sarnia, which decreased the volume of combined sewer overflows and wastewater plant bypasses into the river by an average of 40% from 2006 to 2014
  • investment in an automated system to monitor wastewater flows into Sarnia’s 56 pumping stations to improve flow management and reduce the need for bypasses to the river, at a cost of $1.2 million
  • completion of the Township of St. Clair’s wastewater treatment plant in 2013 at Courtright, downstream from Sarnia, at a cost of $34.5 million
  • eliminated a source of municipal wastewater discharge into the river through the decommissioning the wastewater treatment plant at Corunna

Habitat restoration:

  • eight shoreline projects have restored two kilometers of nearshore fish habitat since 2012, improving access to the river by other aquatic wildlife such as mink  
  • since 2010, over 200 hectares of coastal wetland habitat from Walpole Island to the southern end of Mitchell’s Bay have been enhanced by removing invasive plants, installing habitat structures and planting native plants, providing valuable habitat for fish and wildlife
  • in 2019, Walpole Island First Nation began planning to restore a 675 hectare (1,668 acre) marsh which will include installing a water control structure to optimize water levels and allow fish access for the first time since the marsh was dyked over 50 years ago


A sediment management project is underway to improve sediment and water quality in the three remaining priority areas within the AOC. In 2013, following an assessment study and public consultation, dredging was chosen as the preferred option to clean up mercury-contaminated sediment at the site. Between 2014 and 2018, a committee comprised of Environment and Climate Change Canada, the Ontario Ministry of Environment, Conservation and Parks and Dow Chemical Canada worked to establish a framework for working together and secure funding for a detailed engineering and design plan by spring 2021. The plan will outline actions required and estimated costs to implement the dredging option. The St. Clair Region Conservation Authority will be the project manager for this phase.

Remaining actions

The Government of Canada will continue to work with local and provincial partners to support restoration actions and the environmental monitoring and assessment studies needed to confirm environmental quality objectives are met. Short-term priorities are to:

  • complete habitat restoration actions on Walpole Island and confirm the status of the degradation of fish and wildlife habitat BUI
  • complete the detailed engineering and design phase of the sediment management project
  • continue water and sediment quality monitoring to track progress and guide remaining restoration efforts
  • complete assessments and engage with local communities to confirm the status of the other remaining BUIs


The St. Clair River AOC has made significant progress, and it is anticipated that five of the six remaining BUIs will be restored by 2023. Restoration actions are nearly complete and plans are underway to remediate the three priority areas of contaminated sediment. Under the Canada-Ontario Agreement on Great Lakes Water Quality and Ecosystem Health, the Government of Canada works with the province of Ontario to continue making progress towards remediation, environmental recovery and restoration of beneficial uses. As a binational AOC, Canada and the United States continue to work closely together to achieve delisting. 

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