Combined Sewer Overflow data now available on Open Government Portal

From 2013 to 2017, 890 million cubic metres of untreated sewage and wastewater effluent was released from combined sewer overflows (CSOs) into 844 different waterbodies across Canada. For some context, this equates to untreated sewage flowing over Niagara Falls for 3.7 days, or 88.8 hours. This also means it could fill everyone's bathtub in Canada 148 times. So how do we have such precise numbers? And why is it important to have this information open to the public? 

Where the numbers comes from

This information comes from recently published data on Canada’s Open Government Portal. In 2018, Swim Drink Fish submitted a formal request to Environment and Climate Change Canada (ECCC) to release data in relation to sewage pollution in Canada on the Open Government Portal. The release of this data would provide free, on-demand access to machine readable data files for sewage pollution nationwide. On November 25th, 2019 ECCC released this data that was gathered under Wastewater Systems Effluent Regulations (WSER). This release sets an important precedent publishing other environmental regulatory data for public consumption. 

WSER came into effect in 2012 under the Fisheries Act to help manage wastewater releases by systems that collect an average daily influent volume of 100 cubic metres or more. These regulations relate specifically to subsection 36 in the Act, which is the key pollution prevention provision, that prohibits the deposit of deleterious substances like sewage and wastewater effluent into waters frequented by fish. The work done by ECCC to release this data provides a framework for publishing other environmental regulatory data to the Open Government Portal. 

Turning the Curve on Combined Sewer Overflows

Why are these publicly available datasets so important? Open data are the building blocks of open knowledge. According to the Open Knowledge Foundation open data is vital for information transparency and scientific advancement. Open data means everyone including scientists, policy-makers, non-profits, and the public has access to the same raw materials. The information and knowledge contained in the WSER datasets are key to turning the curve on Combined Sewer Overflows across Canada. The WSER data contains information on when and where sewage is released, and whether wastewater treatment facilities are meeting regulations as they relate to the Fisheries Act. 

Information Contained in the WSER Data

Four different reports were released on the Open Government Portal, all with very important information enclosed:

  1. The Identification Report. This dataset contains detailed information on all the wastewater treatment facilities across Canada. The information ranges from the average volume of effluent deposited per day from wastewater systems, whether the effluent is deposited in water frequented by fish, and also a description of use of water at the discharge point (i.e. recreation like swimming, fishing, boating…).
  2. The Acute Lethality Report. This dataset reports on whether the effluent released from wastewater treatment facilities passed/failed the acutely lethal test for rainbow trout. The Acute Lethality test was developed specifically for determining the acute lethality of effluent from industrial and wastewater facilities.This test is used across Canada by the federal, provincial, and territorial governments to monitor and control industrial and wastewater effluent.
  3. The Monitoring Report. This report contains information on water quality, including results of effluent testing under the Fisheries Act. It tells us whether the effluent released by wastewater treatment facilities is below the accepted limit for suspended solids (SS) and carbonaceous biochemical oxygen demand (CBOD). Both SS and CBOD should not exceed 25 mg/L according to section 6(1) of the Fisheries Act. 
  4. The Combined Sewer Overflow Report. This report contains detailed information about CSOs for all cities in Canada with combined sewer systems (excluding the province of Quebec). The data contains the estimated volume of sewage released on a monthly basis at specified combined sewer outfall locations. The report contains the latitude and longitude for all combined sewer outfalls across Canada. In all, this report provides all the information we need to know when and where, and the amount of sewage released into waterbodies across Canada. 


According to Environment Canada, wastewater is one of the largest sources of surface water pollution in the country. The information contained in these datasets is an important step for Turning the Curve on combined sewer overflows and wastewater pollution in Canada. The knowledge that can be gained from these 4 datasets helps everyone tackle sewage and wastewater problems at both a local and national level. To download all of the reports listed above visit:

Story photo by Flavia Lopez. This photo illustrates one of the impacts of sewage pollution from combined sewer overflows in the City of Toronto. In the photo you can see items that are flushed down the toilet including wet wipes and feminine hygiene products.
Lindsay Telfer
About Lindsay Telfer
Mom, organizer, capacity builder, outdoor enthusiast, justice advocate. Thoughts posted are my own :).
Combined Sewer Overflow data now available on Open Government Portal
Combined Sewer Overflow data now available on Open Government Portal
Imagine a Canada where all waters are in good health: