This is a crayfish. They look a lot like lobsters but live in fresh water. Now that the ice has (mostly) melted from the surface of the lakes, these animals are coming out of their winter hibernation in the mud. Whether they're looking for food, warmth (in the shallows) or territory, I don't know. I do know that they have started moving about and are easily seen in the shallows along the shores, especially if there's a rocky bit of bottom, with places for them to hide.
I'm reasonably sure this fellow (lady?) is Orconectes immunis but that's only a guess on my part based on the sluggish, silty water. This particular specimen measures about 3 inches (7.5cm) long.