Which, according to this diagram, makes him a Red-Eared Slider.
Apparently this species does really well in captivity and has a "clownish, playful demeanor." This makes it a great pet. But, as I mentioned, they can grow to be quite big. This means that pet owners sometimes freak out when their tiny turtle grows bigger than the fish bowl they bought him. So they dump them into the nearest body of water which, of course, their sheltered pet is woefully unprepared for. He doesn't stand a chance, really. . .Judging by the friendliness of this turtle, I wonder if he was formerly a pet. If he was, I hope he's tough enough to make it in the big world.