Canada Day record rainfall sends millions of litres of raw sewage into Ottawa River

Heavy rain flooded a section of Highway 417 in Ottawa’s west end on Wednesday. Environment Canada says Ottawa received more than 100 mm of rain. (Camille Wilson/CTV News Ottawa)

The record-rainfall on Canada Day sent millions of litres of raw sewage flowing into the Ottawa River.

Environment Canada says 118 mm of rain was recorded at the Ottawa Airport on Wednesday, as a series of thunderstorms moved through Ottawa during the afternoon and evening.

The storm flooded dozens of roads and Highways 416 and 417, and the city received over 1,900 reports of flooded basements in homes.

Statistics available on the City of Ottawa’s website shows 218.8 million litres of storm water and wastewater overflowed the sewage system and into the Ottawa River during Wednesday’s storm.

“At the Robert O. Pickard Environmental Centre, which is the city’s wastewater treatment plant, yesterday’s storm resulted in exceptionally high flows, but the plant is operating well today,” Tammy Rose, general manager of infrastructure and waster services, told reporters on Thursday.

It was the biggest one-day overflow since August 10, 2023, when 315.8 million litres of storm water and wastewater overflowed Ottawa’s sewage system.

According to the city’s website, this was the third combined sewer overflow in 2026. 57.9 million litres of storm water and wastewater overflowed the system on June 6, when Ottawa received 21.2 mm of rain. Another 210,000 litres of combined sewer overflow occurred on June 16.

The City of Ottawa built the Combined Sewage Storage Tunnel, designed to intercept and store surface runoff and wastewater until it can be treated at the Robert O. Pickard Environmental Centre and then returned to the Ottawa River. The $232 million project includes six kilometres of tunnels underground designed to stop sewage from flowing into the river during heavy rainfall events.

The underground Combined Sewage Storage Tunnel includes two tunnels: an east-west tunnel through the downtown core from LeBreton Flats to New Edinburgh Park, and a north-south tunnel along Kent Street from Chamberlain Avenue to existing infrastructure behind the Supreme Court of Canada building.

Water quality testing at beaches

Ottawa Public Health no longer tests the water quality at Ottawa’s five public beaches daily, so it’s unclear what the water quality is like for swimming on Friday.

The health unit switched to weekly water sampling last year.

According to the health unit’s website, water samples were collected at Britannia Beach, Mooney’s Bay Beach, Petrie East Bay, Petrie River and Westboro Beach on Monday, and the water quality met the provincial e-coli standard.

The National Capital Commission said the water quality was excellent at its beaches in Gatineau Park. It was last updated on Friday.

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