Many Toronto-area streams are getting saltier and road salt is mostly to blame, conservation experts suggest

Crunching under toe, tire and tread, road salt is used to melt ice and snow for safer surfaces, but recent data shows some Toronto creeks and streams are becoming much saltier, posing risks to aquatic life — and salting may be the culprit.

The 2024 data, shared with CBC Toronto by the Toronto and Region Conservation Authority, shows chloride concentrations in many waterways have been increasing since at least 2015, with Etobicoke Creek and the Don River being among the saltiest.

"We look kind of longer term, and what we're seeing is that of the 47 stations across our jurisdiction, 36 of them are showing increasing trends in chloride over time," said Lyndsay Cartwright, a research scientist with the TRCA. 

"And that's a big concern."

Too much salt can be toxic for fresh water life, and many Greater Toronto Area waterways are over the safe limit, according to the data.

The Canadian Council of Ministers of the Environment (CCME) has guidelines for how salty freshwater can be before it becomes a problem for living organisms. It all comes down to the chloride part of salt. At 120 mg/L of chloride, long-term exposure can cause issues. Past that, things become dire. "When you hit 640 mg/L, species die," said Claire Oswald, Associate Professor of Geography and Environmental Studies at Toronto Metropolitan University. 

"Different aquatic species are going to have different tolerances to chloride, but a lot of the more sensitive ones will die," she said.

Oswald says most of the salt used for winter maintenance works its way through waterways and ends up flushed into the ocean. But, she says, some salt gets stuck in soil and in underground water sources, moving slower through the ecosystem, making salt concentrations a year-round issue.

And that ground water can be well above the safe limits. 

Oswald says her team measured water running off one Mississauga parking lot that had been salted.

"That was over 50,000 mg/L before it went into the sewers and got spit out into the stream," she said.

"It's saltier than ocean water," she added, which has a concentration of around 19,250 mg/L of chloride, according to the CCME guidelines for chloride for the protection of aquatic life. In Toronto, Oswald says her team recently tested soil water next to a road, measuring over 48,000 mg/L of chloride, which she calls "even more shocking" because of how long it will take to work itself through the system.

Overall the numbers are trending up, according to the TRCA. Parts of the Don River hit 7,560 mg/L, Etobicoke Creek peaked at 10,100 mg/L this past year, with waterways, on average, at their highest chloride concentrations in five years according to the TRCA data.

Oswald says her team has been working to find a fix, and it's to put down less salt.