Last month, the NCC officially opened a swim spot off a new dock in Dow’s Lake, part of the Rideau Canal just north of Carleton University. National Capital Commission CEO Tobi Nussbaum, Ottawa Centre MP Yasir Naqvi and others enthusiastically jumped in, partly to demonstrate to the public that the water is safe to swim in and had consistently met safety standards.
As someone who often goes running along the canal and grew up swimming in natural bodies of water, I’ve found myself tempted to jump in after more than a few especially hot runs.
As I peacefully floated on my back in Dow’s Lake, I wondered: What’s the disconnect between how the public feels about this artificial lake and what frequent water testing reveals about its safety?
Why is Dow’s Lake suddenly clean enough to swim in?
For many, the canal’s reputation of being unswimmable dates back decades. After all, Dow’s Lake was once known as Dow’s Great Swamp before it was converted into an artificial lake during construction of the canal, completed in 1832. The city also has a long history of dumping human waste into the Rideau and Ottawa rivers.
However, according to those who study Ottawa’s waterways, Dow’s Lake’s location, depth and vegetation-lined shoreline make it an ideal urban swimming spot.
Additionally, the city has recently invested heavily in infrastructure upgrades, and experts say residents have less to fear about the safety of Ottawa’s waterways than what they may have heard in the past.
Laura Reinsborough, the Ottawa Riverkeeper and CEO of the advocacy organization that conducts testing five days a week at the recently opened site, said water monitoring in the lake began last year, and the NCC selected the site due to its “excellent” water quality.
Since the swimming area was opened, every single water test — which checks for E. coli bacteria levels at the site — has met water quality standards, even after heavy rainfall. Ottawa Riverkeeper shares results in an online swim guide.
Heavy rainfall is a problem because it can wash goose and dog poop and contaminants from city streets — including gasoline, motor oil and pesticides — into waterways.
According to Reinsborough, it’s unlikely the site’s perfect pass rate will last all summer, but a few factors make Dow’s Lake resilient.
“We didn’t expect that it would continue to pass . . . after a rain event, but so far, it has. And we think that might be because it’s a bit of a deeper area of the lake,” she said, adding that the greenery all around the Dow’s Lake shoreline provides some filtering of runoff. ” It’s fairly permeable – The shoreline around there.
“There’s some vegetation that’s been planted,” she said.
This year, in contrast to NCC swim spots monitored by the Ottawa Riverkeeper, Ottawa Public Health has switched from daily to weekly E. coli testing at city-run beaches, which officially opened in late June.
Instead, the city is opting for a daily flag system based on whether a lifeguard is present or not. Still, Kitchissippi Coun. Jeff Leiper recently encouraged residents in a CTV interview to consider passing on beach visits for a day or two after heavy rainfall.
Fact-check: Raw sewage not flowing into Dow’s Lake
Along with washing contaminants from the land into waterways, heavy rainfall can also present a stinky infrastructure challenge.
When it rains very heavily, the city may have to discharge large amounts of stormwater mixed with some sewage into Ottawa’s waterways, also known as a combined sewer overflow (CSO). The alternative is this mixture flooding residents’ basements.
“A combined sewer overflow is a necessary evil to protect residents in large rainfall events,” said Hiran Sandanayake, the city’s manager of water resource planning.
There are 13 sites around the city where CSOs may happen, but out of all these locations, none actually discharges into the canal or Dow’s Lake.
“People don’t understand, and they make all these assumptions… For Dow’s Lake, ‘Oh, it is all sewage.’ No, it’s not all sewage,” said Banu Örmeci, a professor who teaches environmental engineering at Carleton University and is the Jarislowsky Chair in water and global health.
In 2020, the city completed a $232-million combined sewage storage tunnel, designed to reduce the volume and frequency of these events.
Two of the city’s CSO outflows discharge into the Rideau River — Clegg and Springhurst — past where the canal breaks off from the river near Hog’s Back Falls. According to the city, the Springhurst site will soon be decommissioned pending the completion of infrastructure upgrades in the area.
The rest of the CSO sites discharge into the Ottawa River. There have been three CSO events so far in 2025.
The tunnel can store the mixture of stormwater and sewage in areas of the city where sewers were not built with enough capacity to collect the two separately, such as in the downtown core. Then, the mixture can be sent to the east-end Robert O. Pickard Environmental Centre, where it is treated before being safely discharged into the Ottawa River.
Örmeci emphasized the improvement in the city’s sewage system over the years and noted that in the case of an overflow, raw sewage is diluted.
‘It’s exercise. It’s very peaceful. You are in nature. I swim. There’s a duck family swimming with me. So, it’s a wonderful experience. There is no need to be so scared.’
— Banu Örmeci, environmental engineering professor, Carleton University
She also said that water being visibly clear isn’t a necessity for safe swimming.
“Just because the water may be a bit murky, or there are weeds growing in it, you may not want to swim there, but it doesn’t mean that it is unsafe to swim,” she said.
In fact, Örmeci said she often swims in the Rideau River herself due to the overall health and social benefits that come from swimming in a natural body of water.
“It’s exercise. It’s very peaceful. You are in nature. I swim. There’s a duck family swimming with me. So, it’s a wonderful experience. There is no need to be so scared,” she said.
However, Örmeci added that it’s vital to monitor water quality and assess risks for drowning, such as strong currents and water depth. This week, water rescue teams pulled four people from the Ottawa River.
But unlike the Ottawa, Dow’s Lake is an enclosed body of water without many of the risks inherent in a large river system.
