Here's the poop on raw sewage in the Thames River after heavy rain in July

Heavy rainfall has been an ongoing feature this summer in London with the city's wastewater treatment plants and pumping stations struggling against the deluge.

After the downpours brought on by Hurricane Beryl earlier in July, millions of litres of untreated sewage were released into the Thames River.

New city data shows that 21,624 cubic metres of untreated wastewater — about 8.6 Olympic-sized swimming pools — wound up in the Thames on July 15 and 16 when London was inundated with roughly 104 millimetres of rain.

City officials stress that's actually a small amount, and say untreated wastewater going into the river continues to go down as infrastructure and treatment plants are upgraded.

"We treated 400,000 cubic metres on July 15, of which roughly 44,000 cubic metres was partially treated before going into the river," Kirby Oudekerk, division manager of wastewater treatment operations said.

Similar amounts of partially treated sewage were released the following day, on top of the raw, untreated sewage that spilled out.

Sewage running into the Thames River is a problem dating back decades, and one seen around the world, including in Paris. This week, high bacteria levels caused by heavy rain led to the men's Olympic triathlon being postponed in the Seine River. The women's triathlon went ahead on Wednesday. 

Outdated infrastructure like combined sewers – where wastewater and storm drain water flow through the same pipe and become overwhelmed during heavy rainfall – contribute to the problem in London. The city says it is replacing the 12.5 kilometres of remaining combined sewers, and it's also ramping up several stormwater-related projects.

"Really, look as far back as even 10 or 15 years, our raw overflow amounts were much higher," Oudekerk said.

At the same time, partially treated amounts have increased, he said. A vast majority of what is sent to treatment plants during heavy rain is rainwater, which dilutes what wastewater there is.

But it's not just untreated sewage contributing to the river's polluted reputation. Upstream farm runoff is also a factor. 

I probably have more risk eating sushi a couple times a month… than I do eating walleye from the Thames.​​- Robert Huber, Thames Valley Angling Association

A 2022 report from the Upper Thames River Conservation Authority (UTRCA) gave a D grade to its water quality in the city, with phosphorus and E. coli levels above provincial guidelines. Levels have improved since the 1990s, but remained higher downstream, west of Byron.

Robert Huber, president of the Thames Valley Angling Association, said he's not deterred by the data. He regularly eats fish caught in the river, and argues they're likely healthier than Lake Erie fish, which may have more heavy metals.

"I probably have more risk eating sushi a couple times a month… than I do eating walleye from here," Huber said.

The province publishes consumption guidelines for fish from certain waterways, including the Thames.

"A lot of (the wastewater) gets washed downstream really fast, it doesn't really change the quality of the fishery," Huber said. 

The city is adding storage facilities to treatment plants that would hold potential overflow until it can be treated, Oudekerk said. It doesn't add capacity, though, which is needed as the city grows.

Of London's five treatment plants, Greenway treats 60 per cent of the city's wastewater. The facility is undergoing climate change-related upgrades.

Most of the plants are decades old, but they have been upgraded. Oudekerk says the city is looking to replace the Pottersburg plant sometime in the next three decades.

The city is developing a website for easier access to wastewater data. It's expected to be online later this year.