I swam in Lake Ontario near Kingston from the mid-80's up to a few years ago and never had an issue, although after heavy rains in summer there could be pretty high E. coli load near shore due mostly to ducks and geese (solution, swim off a dock).
Fecal matter from birds--like the scads of corrmorants around Kingston--is rich in nutrients, and while agricultural runnoff can be a problem Lake Ontario doesn't suffer from it particularly, and even without it there are plenty of altnernative nutrient sources.
Fecal matter from birds--like the scads of corrmorants around Kingston--is rich in nutrients, and while agricultural runnoff can be a problem Lake Ontario doesn't suffer from it particularly, and even without it there are plenty of altnernative nutrient sources.