It could be that it is simply a drainage ditch from fields, which it looks like to me. I don't know where that is but several areas of ontario had a lot of rain. I doubt its a sewage runoff...that would be a hell of a lot toilets flushing to produce that much water
It could just contain what was on the field (pesticides, herbicides), which will turn the plants red and yellow. The local conservation authority will know what to do.