Midland Water Snake

I think this is what this is--we were walking through Naperville on the Riverwalk and saw this guy swimming along up in the section by the pool (further downstream were wading fishermen, who I am sure would have been a little put out by seeing this guy swim by.

I don't mind snakes if I know what they are, like the little ribbon snakes that live in our backyard, but the markings on this one made me glad I was up on the bank using a telephoto zoom.