St. Catharines Combined Sewer Overflows at Niagara Region Facilities

Data presented here is updated every three months. The data contains records from
April 01, 2024 to March 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 Mar 5, 2025 7.500 ML Heavy Precipitation
Port Weller Plant Mar 5, 2025 17.025 ML Heavy Precipitation
Port Weller Plant Feb 27, 2025 2.251 ML Heavy Precipitation
Snow Melt
Port Weller Plant Feb 25, 2025 6.762 ML Snow Melt
Port Weller Plant Feb 24, 2025 1.213 ML Snow Melt
Port Weller Plant Dec 29, 2024 0.499 ML Heavy Precipitation
Port Weller Plant Dec 10, 2024 0.043 ML Heavy Precipitation
Port Weller Plant Dec 9, 2024 0.006 ML Heavy Precipitation
Port Weller Plant Oct 29, 2024 0.801 ML Heavy Precipitation
Port Dalhousie Plant Sep 9, 2024 2.410 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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