Combined Sewer Overflow volumes from wastewater systems subject to the Wastewater Systems Effluent Regulations

The Wastewater Systems Effluent Regulations (WSER), developed under the Fisheries Act, came into force in 2012 to manage wastewater releases by systems that collect an average daily influent volume of 100 cubic metres or more. The WSER also does not apply to any wastewater system located in the Northwest Territories, Nunavut and north of the 54th parallel in the provinces of Quebec and Newfoundland and Labrador. The WSER set national baseline effluent quality standards that are achievable through secondary wastewater treatment.

The WSER require owners or operators of wastewater systems with combined sewers to submit an annual report on the total volume and the number of days wastewater is discharged per month via combined sewer overflow (CSO) points as a result of precipitation.

The map below shows the volume of effluent (in cubic metres) discharged in a year from all CSO points situated within the collection area of a wastewater system. For the most part, the volumes provided to ECCC are estimates.

Please note, a value of “999999999” in the dataset indicates that the volume data is unavailable and it does not mean that a volume of 999,999,999 m3 was released within the collection area of a wastewater system.

The map is available in both ESRI REST (to use with ARC GIS) and WMS (open source) formats. For more information about the individual reporting wastewater systems, datasets are available in either CSV or XLS formats.

Data from Quebec

As of 2018, no combined sewer overflow volumes from Quebec municipalities are available since an equivalency agreement is now in effect.

More information on the wastewater sector including the regulations, agreements, contacts and resource documents is available at: https://www.canada.ca/wastewater

Data and Resources

Additional Info

Field Value
Last Updated April 17, 2026, 21:55 (UTC)
Created April 17, 2026, 21:55 (UTC)
contact_email eu-ww@ec.gc.ca
contact_person {"fr": "Gouvernement du Canada; Environnement et Changement climatique Canada,ec.enviroinfo.ec@canada.ca", "en": "Government of Canada; Environment and Climate Change Canada,1-800-668-6767,ec.enviroinfo.ec@canada.ca"}
criticality_level []
data_dictionary ["environment"]
geographic_scope []
open_canada_collection fgp
open_canada_date_published 2022-03-01 00:00:00
open_canada_keywords {"fr": ["Test réglementaire", "eaux usées", "eau", "rejet", "effluent", "eaux-vannes", "SIRRE", "RESAEU", "surverses des égouts unitaires", "surveillance", "rapports", "traitement", "Loi sur les pêches", "substances nocives", "pollution de l'eau", "qualité de l'eau", "Eaux usées", "Règlements", "Évaluer la toxicité de la présence dans l'environnement des substances et des déchets dangereux; les gérer et les surveiller", "Planifier et mettre en œuvre l'infrastructure de surveillance dans le but d'évaluer la présence et les niveaux de substances préoccupantes", "National (CA)", "Direction générale de la protection de l’environnement", "Direction des secteurs industriels et des substances chimiques", "3.1.2 Gestion des effluents", "Non Classifié"], "en": ["Statutory Instrument", "wastewater", "water", "discharge", "effluent", "sewage", "ERRIS", "WSER", "combined sewer overflow", "monitoring", "reporting", "treatment", "Fisheries Act", "deleterious substances", "water pollution", "water quality", "Waste water", "Regulations", "Assess Toxicity; Manage and Monitor for Environmental Presence of Hazardous Substances and Waste", "Plan and Implement Monitoring Infrastructure to Assess Presence and Levels of Substances of Concern", "National (CA)", "Environmental Protection Branch", "Industrial Sectors and Chemicals Directorate", "3.1.2. Effluent Management", "Unclassified"]}
open_canada_subject ["nature_and_environment"]
sensitivity_level unrestricted
title_fr Volumes des points de débordement des égouts unitaires des systèmes d’assainissement des eaux usées assujettis au RESAEU
update_frequency P1Y