You won't find much in the way that will leave you wanting to stay out of the waters here in the Great Lakes. The description of the biggest predator in the Great Lakes may drive you to at least do it during the day if anything... Michigan's biggest predator in the Great Lakes is a Sea Lamprey.
The organisms living on the bottom in shallow waters are the same kinds of snails, clams, worms, mayflies, and caddisflies found in most small lakes. The deep waters, however, are the realm of some organisms that are found only in the deep, cold lakes of the northern latitudes.
Alligators are rarely found in the Great Lakes. Although some alligators thrive in freshwater, it's just too cold in the north for them to survive. They don't typically live farther north than North Carolina. It's unclear how the alligator arrived to Lake Michigan.