Ronto along the Erie Stretch fascinated me in Fallout 3's "The Pitt" DLC - obviously it's Toronto, and obviously it's inhabited at least enough that the place has a name. We know nothing about it otherwise, which means I can fill it with whatever monsters I like.

Rainbow sharks are the largest aquatic predators in the post-War Great Lakes system, descended from steelhead that survived the rampant pollution of the lake systems in the decades leading up to the Great War. Mutated by the millions of barrels of toxic waste dumped into the lakes, these strong, fast fish can grow to fifteen feet or longer, feeding on great lakelurks, other large fish, unwary divers, molluscs, and various detritus - they behave rather like modern tiger sharks in that they will investigate most objects for edibility by taking a bite. Their teeth have fused into two long dental plates that are as sharp as cleavers and can bite through steel. Hooking a rainbow shark is typically accidental, as few things aside from high-caliber weapons can kill them, and you really don't want to be firing those in a boat - a cut line is a small price to pay for living to fish another day.