Above image: Impacts of CSOs into the Toronto Harbour at 3:26pm July 17th, 2018, following 8 mm of rain. Captured from the CN tower EarthCam by Swim Drink Fish.

It’s important to be transparent that this Shared Measurement System was designed from a non-Indigenous worldview and we recognize that Indigenous ways of knowing are absent from it. For more information on this positioning, see our Right Relations page.

Overview

Untreated sewage can end up in our waterways in multiple ways. Combined sewer overflows (CSOs) are one major source, where pipes that carry wastewater from our houses and businesses also carry stormwater to treatment plants. In heavy rainstorms, more of this combined water than the treatment plant can handle accumulates, activating overflow points that redirect untreated water into our waterways- our rivers, lakes and oceans.

The OLW Network is tracking this measure in three ways: how many CSO locations exist across the country, how many municipalities have them, and what the volume of the untreated sewage entering our waterways is.

In 2015, a reported 1,516 combined sewer overflow locations existed across 130 municipal systems, and according to Statistics Canada, that year, 168,800,000 cubic metres of untreated sewage were released from CSOs into the water. Across Canada 268 municipal systems are required to report CSO discharges, however many do not report accurate data concerning the volume and rate of sewage releases to Environment Canada, making this number likely an underestimate. For example: in 2015, only 36 of 168 municipal systems in the province of Quebec filed completed combined sewer overflow reports; some municipal systems filed a record of overflow events but did not report any volumes.

To request a copy of CSO overflow data for your community, please email OLW Network member Swim Drink Fish at: [email protected].

Last updated August 2019