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Châteauguay River – Monitoring water quality and detecting sources of pollution, phase 2

Châteauguay River – Monitoring water quality and detecting sources of pollution, phase 2

Strong swimming potential confirmed after two years of study

Following his study of the microbiological quality of water aimed at developing the swimming potential of the Châteauguay River carried out in 2021, the Fondation Rivières was commissioned again to confirm the preliminary results. This time, the Foundation identified the sources of contamination, provided avenues for intervention and established a preliminary safety protocol with a view to improving public access to water in the Mercier sector.

The Châteauguay River in Mercier. Photo: Fondation Rivières


  • Validation of bathing potential
  • Site vulnerability assessment – bacteriological water quality
  • Continuous monitoring of water quality
  • Screening for main sources of pollution

Partners and collaborators

Our methodology

Regular tracking sites
Testing sites

Supported by the Châteauguay Zone Conservation and Development Society (SCABRIC), the Fondation Rivières carried out regular, high-frequency sampling, in addition to screening tours. These efforts made it possible to determine the water quality at the study sites and to establish contamination trends.

The samples were analyzed by countingEscherichia coli (E.coli) traditional. The Fondation Rivières carried out hybrid monitoring of the water quality of the Châteauguay River, using both traditional analyzes ofE.coli in the laboratory at the Eurofins Environex Longueuil laboratory and using rapid analysis technology.

The latter, the ColiMinder device makes it possible to detect in 15 minutes the presence ofE.coli in water by enzymatic analysis. Including the data collected during the 2021 preliminary study, the Fondation Rivières collected a total of 271 laboratory measurements (CFU/100 mL) which can be correlated to enzymatic readings, taken by the ColiMinder device. This approach made it possible in particular to establish a correlation between the enumeration ofE.coli in the laboratory and ColiMinder measurements in the Mercier sector, which could serve as a “first rapid alert” mechanism to signal contamination peaks.

The 4 main stages

Sampling took place over a period of 12 weeks, between July and September 2022.

  • July 11 – Start of regular monitoring on two sites and screening activities
  • August 12 – Added a third regular tracking site
  • September 30 – End of monitoring and screening in the field
  • December 12 – Submission of the report to the City of Mercier



In summer and in dry weather, the water quality is excellent, allowing swimming and the practice of non-motorized water activities (canoeing, kayaking, paddle boarding, etc.).


Only the sector downstream of the river (City of Châteauguay) appears to present a risk of contamination in dry weather.


Water quality deteriorates from mid-September, probably due to spreading on agricultural land.

Measures to protect the Châteauguay River will allow swimming and water activities for years to come!

The City of Mercier is investing in the future of the Châteauguay River

The City of Mercier showed initiative by participating in this study on the water quality of the Châteauguay River. This type of project aims not only to monitor and improve the quality of the territory's water, but also to facilitate public and safe access, as targeted by the most recent five-year review. of the Mercier urban plan (p.22). The findings of this study allow the City to guide its interventions and contribute to the preservation of the Châteauguay River.

Do you make decisions within your municipality?

Consult the guide to opening an urban swimming site to find out how the Fondation Rivières can help you.

Plage de Verdun
Verdun beach in summer 2021

Our water quality monitoring mandates

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