I believe that in our area (Central Ontario)painted turtle are native,while red ear sliders are pet releases that don't breed because of the cold.I wouldn't be able to tell these apart at a distance.Our snappers (also called mud turtles here) are a whole different matter.
A large painted might go 5-6" front to back of the shell. They will also have red or yellow stripes on their head.You will see them sunning themselves on rocks or logs, sometimes 5 or 6 at once. Our snappers normally only leave the water to lay eggs (although I once saw one on a log).They have a lighter rough brown shell as opposed to the dark green/brown smooth shell of the painted. If you do drag one out of the water they will quite often have leeches on them and if you hold a stick in front of a captive snapper you will see how they get their name.
Whenever I find one on our driveway I transport it as we have kids, pets and water birds around that give me a lot more pleasure.....
A large painted turtle might draw blood but a 8" snapper could take a finger.
