While most residents hunker down when a snowstorm hits, Ottawa Riverkeeper’s volunteers reach for their parkas. For the past five years, they’ve been heading out to collect water samples during nasty weather, measuring the impact of road salt on urban creeks.
“Road salt is toxic to aquatic environments,” explains Larissa Holman, Director of Science and Policy for Ottawa Riverkeeper. That’s because salt contains chloride.
Too much chloride kills zooplankton, a key food source for many aquatic organisms such as amphibians, fish and invertebrate species. Frogs have very permeable skin that makes them particularly sensitive to chloride. And even moderate increases in chloride can impair the development of insects like dragonflies.
Ottawa Riverkeeper volunteers collecting data. Image source: Ottawa Riverkeeper.
But the City of Ottawa wasn’t tracking chloride data during winter months. So, Ottawa Riverkeeper stepped in, launching a community-based monitoring initiative.
Volunteers collected data within 48 hours of “trigger events” — like snowfalls, freezing rain or major thaws — that could create salty runoff. Volunteers now also collect data at regular intervals throughout the winter.
Between 2020 and 2024, Ottawa Riverkeeper volunteers collected 500 samples at 45 different locations across Ottawa and Gatineau. And what they found paints a grim picture.
Nearly half of their samples had chloride levels above 640mg/L — enough to cause immediate harm to freshwater organisms. 90 per cent were above the 120 mg/L threshold for chronic toxicity, which can do damage if those concentrations persist for extended periods.
And summer monitoring revealed elevated chloride levels long after the ice and snow had disappeared.
Ottawa Riverkeeper volunteer collecting data. Image source: Ottawa Riverkeeper.
Addressing road salt misconceptions
Holman understands the importance of keeping streets, sidewalks and driveways ice-free. A slip a few winters ago left her with a broken wrist. “But overusing salt is not the solution,” she stresses.
Much of the 5.5 million tonnes of road salt used across Canada each year is unnecessary.
Road salt lowers the freezing point of water to keep it from turning to ice. However, when applied as it is, it starts losing its effectiveness at minus 7 degrees Celsius and stops working completely below minus 10, so there’s no point in applying it in colder temperatures.
Even when the conditions are right, just two tablespoons per square metre will do the job — and adding more won’t create better results.
City of Gatineau sign indicating a salt-free zone. Image source: Ottawa Riverkeeper.
Driving lower-salt solutions
To boost awareness about the issue, Ottawa Riverkeeper shares their findings on DataStream. “If anyone’s looking for chloride data and they select that parameter, our data is going to pop up,” Holman says. “Hopefully that will help drive some interesting conversations.”
Ottawa Riverkeeper also posts their protocols on their website, making it easy for other groups to start their own salt-monitoring program. And Holman regularly talks to winter contractors, municipal councillors and condo boards about smart salt use.
Those efforts are paying off.
Last winter, the City of Gatineau introduced designated salt-free areas near fragile ecosystems. Meanwhile, the City of Ottawa is reviewing their road salt practices, prompted by Ottawa Riverkeeper’s work.
“That is super encouraging,” says Holman. “I don’t feel like we would be having the same conversations with decision makers and individuals if we didn’t have data to support it.”
View Dataset: https://doi.org/10.25976/d24n-qg67
