St. Catharines Combined Sewer Overflows at Niagara Region Facilities

Data presented here is updated every three months. The data contains records from
August 01, 2024 to July 31, 2025.

Volume is measured in megalitres. (1 megalitre = 1 million litres)

CSO Location Date of Overflow Volume (ML) Reason for Overflow
Port Weller Plant Jun 30, 2025 1.598 ML Heavy Precipitation
Port Weller Plant Jun 18, 2025 1.728 ML Heavy Precipitation
Port Weller Plant Jun 18, 2025 12.516 ML Heavy Precipitation
Port Dalhousie Plant Jun 18, 2025 8.838 ML Heavy Precipitation
Port Weller Plant Jun 18, 2025 3.259 ML Heavy Precipitation
Jordan Valley Sewage Pumping Station May 22, 2025 0.043 ML Heavy Precipitation
Port Dalhousie Plant May 22, 2025 25.834 ML Heavy Precipitation
Port Weller Plant May 21, 2025 47.633 ML Heavy Precipitation
Port Weller Plant May 21, 2025 32.902 ML Heavy Precipitation
Port Weller Plant May 16, 2025 0.775 ML Heavy Precipitation
More Locations

Historical Overflow Data for St. Catharines

202420232022
Total Overflows: 49
Total Volume: 540.101 ML 		Total Overflows: 44
Total Volume: 545.552 ML 		Total Overflows: 34
Total Volume: 761.968 ML

Overflows contain mostly Storm Water

While the volume of an overflow may seem large, the amount of untreated sewage present in the overflow is small when compared to the amount of stormwater or snow melt.

Niagara typically treats about 80,000 megalitres of sewage each year.  The vast majority of wastewater discharged into the sewer system receives full treatment and only a small percentage of this sewage overflows. These overflows usually only occur during periods of heavy rain or during seasonal snow melts.

Historical Data

If you require more detailed information about a specific combined sewage overflow, you can contact the water & wastewater division.

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