One of the most detailed investigations ever conducted in Canada into the fate of road salt has found that it is polluting groundwater and causing some streams during winter thaws to have salinity levels just under those found in the ocean.

The elevated salt readings were detected in Pickering, where researchers from the University of Toronto have been studying how the salt spread on highways, such as the 401, and other roadways through suburban sprawl affects water quality. They found that so much salty water from the community is ending up in Frenchman's Bay, a scenic lagoon on the shores of Lake Ontario, that the small water body is being poisoned.

"Our findings are pretty dramatic, and the effects are felt year-round," said Nick Eyles, a geology professor at the university and the lead researcher on the project. "We now know that 3,600 tons of road salt end up in that small lagoon every winter from direct runoff in creeks and effectively poison it for the rest of the year."

He called the findings, which were published recently in the journal Sedimentary Geology, "a really bad-news story" involving a "relentless chemical assault on a watershed."

The Pickering area provided researchers with an ideal place to study the effects of road-salt spreading, because most of the city lies within a relatively compact 27-square-kilometer watershed, where it was easy for pollution monitors to track where salt spread on roads ended up.