I saw this guy last week on a kayak trip down a local river, the Little Miami (in southwest Ohio). It is a Spiny Softshell Turtle, Trionyx spiniferus. The females get up to 17" long, the males are smaller. This one was about 10". Except for seeing them basking, these turtles are all about stealth, and you rarely see them in the water. The shell blends in to muddy or sandy bottoms, and the snorkel nose allows them to get a breath without being seen.
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