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Water quality of the Châteauguay River: excellent swimming potential confirmed after two years of studies

Rivière Châteauguay, dans le secteur de Mercier


Montreal on June 8, 2023 – In this Water Month, the Fondation Rivières, the City of Mercier and the Society for the conservation and development of watersheds in the Châteauguay area (OBV SCABRIC) make public the results of a study which confirms that the water of the Châteauguay River, in the Mercier sector, is of excellent quality for swimming and practicing non-motorized activities (kayak, canoe, paddle board, etc.) in complete safety, in summer and dry weather. 

A period of dry weather corresponds to any day for which precipitation over the last three days, including the current day, is less than 5 mm. In rainy weather, water quality is variable since overflows from sanitation networks can affect it, as is the case in many places in Quebec. After mid-September, water quality deteriorates, probably due to spreading activities. 

A second study in Mercier

Granted by the City of Mercier, this contamination source screening study follows a preliminary water quality monitoring study carried out in 2021, in which the City of Châteauguay also participated. The 2021 study showed that in Mercier, the water was of good quality throughout the summer outside of periods of rain but contamination in dry weather had been detected in the territory of Châteauguay, just downstream by Mercier.

The Fondation Rivières and OBV SCABRIC invited the towns of Mercier and Châteauguay to further investigate the sources of pollution in the river. The City of Mercier has agreed to collaborate again with Fondation Rivières in order to be clear about water quality. This time, the Foundation carried out closer monitoring in collaboration with OBV SCABRIC. The work carried out made it possible to identify sources of contamination, develop avenues for intervention and establish a preliminary safety protocol with a view to improving public access to water in its sector. 

Watercourses and ditches under the magnifying glass

Watercourses and ditches were identified as a vector of contaminated water to the Châteauguay River, but their contributions were quickly diluted by the river. The Fondation Rivières nevertheless recommends controlling the quality of the agricultural riparian strips along the river and its tributaries (watercourses and ditches) as well as inspecting and bringing deficient septic installations up to standard. 

“The collaboration of the City of Mercier has been remarkable and we salute their concern for the protection and development of the Châteauguay River,” says the general director of Fondation Rivières, André Bélanger. 

The general director of OBV SCABRIC, Geneviève Audet, adds: “Such initiatives fit perfectly into the objectives of the water master plan for our territory and into the promising projects for the region aimed at making the Châteauguay River more accessible and more attractive for nautical tourism activities.

“This type of project aims to monitor and improve the quality of water in the area, and the positive results encourage the City to continue its efforts to facilitate public and safe access, as targeted by the most recent five-year review of the sustainable urban planning plan for the City of Mercier. The results of this study will allow the City to guide its interventions and contribute to the preservation of the Châteauguay River,” says Lise Michaud, Mayor of Mercier.


The Fondation Rivières and the OBV SCABRIC sampled water from the river at three sites in the Mercier territory between July 11 and September 30, 2022. The analysis was carried out on the basis of the count ofEscherichia coli (E.coli) and enzymatic analyses. 

Approximately 95% monitoring measurements from all sites studied met the threshold for indirect contact activity between mid-July and mid-September. In Quebec, the recommended threshold for swimming is 200 CFU/100 mL while that for indirect contact activities is 1,000 CFU/100 mL. 

This project was funded by the Saint-Laurent Action Fund (FASL) and his Maritime Tributaries Program, coordinated by the Grouping of Quebec watershed organizations (ROBVQ) and carried out thanks to the financial support of the Government of Quebec as part of Avantage Saint-Laurent, the new provincial maritime vision.

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Logos programme Affluents Maritime, Fonds d’action Saint-Laurent (FASL), Regroupement des organismes de bassins versants du Québec (ROBVQ) et gouvernement du Québec
Picture of Sophie Lachance

Sophie Lachance

Communications and Mobilization Manager
Fondation Rivières
514-272-2666, ext. 307

Communications Branch
City of Mercier
450 691-6090, ext. 276

Photo: Châteauguay River in the Mercier sector by the Fondation Rivières

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