Community Science – Road Salt Monitoring

Article by John Challis

In July 2023, Gravenhurst Town Council passed a bold resolution recognizing road salt as a toxic substance, echoing a 2004 addition to the Canadian Environmental Protection Act. Council vowed to reduce its use “as much as possible while maintaining safety on roads and sidewalks.”

Road salt, of course, is seen as an absolute winter necessity. Since the 1950s, it has been used to make icy roads safe, at the speeds we all expect we should be travelling. But it creates more problems than it solves. It’s costing billions to fix salt damage to bridges and roads. Our cars corrode, forcing major expenses. Salt has even been found in private drinking water wells.

The environmental harms are every bit as problematic; dying pines facing Highway 11 are evidence of that. It’s been on the radar of the Friends of the Muskoka Watershed (FOTMW) for better than a decade.

FOTMW calculates there are roughly 30,000 tonnes of road salt in Lake Muskoka. Dr. Norman Yan, founding director of FOTMW, worries about salt’s impact on aquatic life. He affectionately refers to the 80 known species of zooplankton in the lakes as “nature’s lawnmowers.” They chow through algae in astounding volumes. But some are vulnerable to elevated chloride, the dissolved element from road salt.

Too much reliance, Dr. Yan says, is put on the Canadian Water Quality Guideline, which sets a chloride limit of 120 mg/L in water bodies. FOTMW, working with Queen’s University researchers, conclude that concentrations of 10 mg/L are likely toxic to some key lake biota – the level present in 20 per cent of our lakes.

It’s a warning that Muskoka’s legendary water quality is vulnerable.

Municipalities haven’t been ignoring the issue. Gravenhurst has switched exclusively to sand on sidewalks and municipal parking lots and is working on reducing quantities on roads. The District of Muskoka has been monitoring chloride in our lakes since around 2004.

But there’s more work needed. This is where citizen science comes in. The FOTMW feels recruiting local residents to test for evidence of road salt in urban runoff can add significantly to our understanding of where and when road salt is problematic. 

FOTMW recruited their first 10 citizen scientists to run a pilot program in the winter of 2022-2023. Among the recruits were members of the Gull and Silver Lake Residents’ Association. Already concerned about road salt, the association was eager to take on the role of pilot monitoring.  Joanne and Clarke Smith jointly chair the environmental committee with the Gull Lake group. They’re a good fit for the portfolio: she a high school science teacher with training in zoology, he a retired lawyer. They received test kits to use at three sites in Gravenhurst.

“The main concern of the association has always been the quality of the water,” Joanne says.

Chloride has become a growing part of that focus. They discovered snow cleared from plaza parking lots on Bethune Drive was piled beside a storm drain that fed salt-laden meltwater into the lake. Highway 11’s bridge over the lake allows meltwater to drain salt into the water as well. And various municipal roads contribute more salt.

Thanks to newer technology, the citizen scientists’ task of measuring salt is not that complicated: Find some open water and pull out a cupful. An electronic probe does the analysis.

The probe is a fascinating tool that provides accurate assessments of the chloride in the water. The salt in lake water is not something you can taste: the levels are in parts per million. Instead, Dr. Neil Hutchinson of FOTMW explains, the pen-sized electronic probe “uses conductivity, an accepted means to estimate chloride.”

The chloride measurements the Smiths and others have compiled have them worried.

“We knew the lake had soft water,” Joanne says. “But we never thought of the effects chloride would have on soft water.” The science has revealed a “multitude” of impacts in the lake. It’s exactly the kind of synergy the FOTMW was hoping for when this program was designed.

“Citizen scientists are our eyes on the watershed,” says Dr. Hutchinson “They live close to runoff areas and can mobilize quickly and take measurements in response to rain, snow or thaw events when they occur. They are also proactive – making sure that staff and politicians hear the concerns from citizens as well as scientists.”

Dr. Hutchinson has been monitoring a feeder stream leading to Jevins Lake, just downstream from Highway 11’s bend around the lake at Gravenhurst. He’s been using a slightly more sophisticated conductivity monitor, called a Hobo Logger, which remotely records measurements every five minutes. It’s been keeping a record for the better part of a year. Road salt runoff has easy access from the highway to the lake here, as well as from the town’s large south commercial area, with its major retail outlets. Dr. Hutchinson’s results show that during thaw periods from February to May meltwater created sharp spikes in chloride levels, approaching the Canadian Water Quality Guideline.

Jevins Lake, Joanne Smith says, “is a red flag.” She and Clarke have measured runoff in a ditch leading from the commercial area, and last year recorded the highest readings of all sites. The ditch feeds water into a wetland complex that leads to Dr. Hutchinson’s “Hobo site,” which in turn leads to Jevins Lake.

Clarke Smith says it’s understandable that salt gets a lot of use in commercial retail parking areas. It’s a liability issue. But Joanne points out the amount being used far outstrips what is needed.

“It only takes a tablespoon of salt to melt a square metre of ice,” she says. And putting salt down in the coldest weeks is pointless: below –12°C, salt loses its ability to melt ice.

Even in its infancy, the road salt pilot has had unexpected benefits.

“In addition to more data being collected,” Spencer MacPherson, citizen science co-ordinator with FOTMW, says, “we have already seen benefits of creating a small community of motivated individuals with a common goal. Some of our volunteers have really stepped up and helped us make some positive changes to the program for this upcoming season.”

The chance to play an important part in the project is what drew Joanne and Clarke Smith to get involved. It’s a commitment to community, Clarke says, a belief he holds that “by having people involved, change happens.”

And, Joanne enthuses, “it’s practical research. I mean, how wonderful is that?”

Other initiatives are also underway. Dr. Hutchinson, working with the Muskoka Watershed Council, has used the District of Muskoka’s data on chloride levels in more than 200 lakes to document the status of road salt for the Muskoka Watershed Report Card, released on September 18. He is working with the FOTMW to develop a recommendation for a more sensitive, Muskoka-specific water quality guideline for chloride, incorporating the enhanced toxicity of road salt in Muskoka’s soft water.

If that comes about, it could dramatically affect the way road salt is used in the District of Muskoka. The program will continue to expand to new sites, with the help of new recruits.


If you’d like to become one of the citizen scientists working on this project, contact Spencer MacPherson at, or by phoning the Friends of the Muskoka Watershed office at 705-640-0948.