According to the to Guide Eating Ontario Sport Fish – Page 12 . . .
Clams
Although freshwater clams are often readly available in many Ontario water bodies, it is advised that they are not consumed. Clams are filter feeders and therefore they are usually low in chemical contaminants, but for some reason, they can harbour harmful bacteria and other pathogens. If they are not suffeciently cooked, they may cause health problems, such as food poisoning.
Hope this helps.