Thorold Combined Sewer Overflows at Niagara Region Facilities

Data presented here is updated every three months. The data contains records from
May 01, 2025 to April 30, 2026.

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

Historical Overflow Data for Thorold

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.