Water quality in waterways

Last updated February 5, 2024

The city ensures the quality of its waterways and protects their ecosystems and biodiversity through its three-fold action plan: Reduce pollutants at source, intercept and treat wastewater, and monitor the aquatic environment. Here’s what you need to know.

The city has created several ways to monitor water quality in Montréal. Reduction at source of pollutants, wastewater discharge controls and monitoring aquatic environments help protect ecosystems and biodiversity.

Reduce pollutants at source

Before discharging wastewater or contaminants into the sanitary sewer system, companies and dental offices must request a permit. To receive one, they must provide the city with proof that their equipment complies with the criteria for obtaining a permit and current regulations. Once a permit has been granted, the city will verify that regulatory requirements and standards are respected. For example, it may take samples to measure the quantity and nature of pollutants discharged.

Accidental discharge

Immediately notify the city of an accidental discharge. The causes of the discharge as well as measures implemented to prevent it from recurring must be provided within 15 days.

Intercept and treat wastewater

The city’s wastewater treatment station is designed to reduce concentrations of particulate matter and phosphorus in wastewater generated on the island of Montréal. Although its process is not specifically adapted to reduce other contaminants, it does reduce the chemical oxygen demand (COD) and metal concentrations by around 50 per cent. Consequently, a number of factories on the island of Montréal must treat their own industrial wastewater that is high in metals or other contaminants before releasing them into the sewer.

Industrial wastewater fees

With a view to tax equity with residents, companies with large wastewater and high concentration of pollutants must assume the costs of treating their effluents. Fees for industrial wastewater discharges are determined according to the volume of wastewater that the factory releases into the sewer system, its concentration of particulate matter (PM), its totale concentration of phosphorus, its cheminal oxygen demand (COD) and, if applicable, increased difficulty of treating effluents (required alun dosage). 

Monitor the aquatic environment

The job of monitoring the aquatic environment comes under the wastewater treatment program. The various sampling programs created by the Réseau de suivi du milieu aquatique (RSMA) evaluate the overall quality of the waterways (COURDO), the quality of the water along the shoreline (QUALO), the quality of streams and inland waterways (RUISSO), and the quality of water in the storm sewer network (PLUVIO). Some 500 stations collect water samples. These sites, spread out over several locations, were chosen based on recreational and wildlife considerations or their proximity to storm sewer outfalls and the mouths of streams. Sample results for specific dates are published on this map (in French). The parameters analyzed under the RUISSO and COURDO programs and the RSMA’s annual report can be viewed online.

Reporting an issue

You can report a situation relating to a waterway or sewer that seems abnormal or suspicious. Complaints are analyzed within 24 working hours, or on Monday if they are sent during the weekend. In case of an emergency, a team will go to the site rapidly. You will be advised of the measures taken.

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