Road salt levels in southern Ontario waterways have hit record highs, making some as salty as the ocean, environmental advocates said Wednesday as they called for measures to mitigate the impact on species and ecosystems.

World Wildlife Fund Canada said its new maps tracking chloride from road salt show levels in many rural and urban southern Ontario waterways are increasing dangerously.

Salt's chloride component is toxic to freshwater species and ecosystems, compromising habitats for fish, frogs, mussels and other creatures, and endangering their survival during the spring and summer spawning season, the organization said.

"Basically it's lethal levels of salt we're seeing," said Elizabeth Hendriks, WWF Canada's vice-president of freshwater.

She said healthy levels for aquatic life should be less than 120 micrograms per litre, but the maps show some areas in southern Ontario currently have levels greater than 1,000 micrograms per litre.

Hendriks said a few years ago, people found a blue crab in Cooksville Creek in Mississauga, Ont., and couldn't explain how it got there.

"Blue crab is an ocean crab but it was thriving a freshwater stream. So how do we begin to reverse that trend?" she said.

More than 7 million tonnes of road salt used each winter

The maps released Wednesday are based on provincial data collected during the summer months and allow researchers to compare chloride levels going back roughly a decade, according to WWF Canada. The most recent numbers date back to 2016.

More than seven million tonnes of road salt are used in Canada each winter by public road agencies, while use by small towns and private sector companies is not currently tracked in Ontario, the organization said.

The federal government has released standards on the use of road salt but those are not the same as regulations, Hendriks said. The Ontario government, meanwhile, has listed salt contamination as a major issue in its environmental plan, she said.

It's important to work with the private and commercial organizations as well to get them to reduce their salt use, she said.

Residents, too, are overestimating how much salt is needed, Hendriks said, adding it only takes the equivalent of a small pill bottle to melt ice from a city sidewalk slab.

"People just don't often connect that what we do on the land, especially in winter when we're not thinking about our lakes and streams as much ... [with how it] impacts our lakes and streams," she said.

"That salt doesn't disappear come spring, it just flows into our lakes and rivers."