Old Tom & I have been up fishing in and around the park this week. Yesterday we ran into two of these guys on Straight Fork within about 200 yards. Can anyone ID?

Just trying to look at other pictures online, it seems like the most likely candidate is a Northern Water Snake, but this one doesn't seem to have the full bands like the other pictures I can find. A larger picture is here:
http://www.flickr.com/photos/2571720...81273/sizes/o/
We were fishing another pretty large flow outside the park at an elevation of around 3500. I was fishing by myself and heard something rumbling (more like clacking) upstream from me. At first I thought it was a stump or other big piece of wood. It was actually a big turtle tumbling through a rough bit of water. I got a good look at it once it got into the slower water at my feet. The thing was the size of a serving dish, with the shell maybe 14 or so inches from front to back. If I was home, I would have said it was a snapping turtle, as it certainly looked the part to me, but that's something I associate with farm ponds and golf course water hazards, not high elevation streams. Do snapping turtles occur up there & this far west (Macon Co)? If not, any other good candidates for this turtle?
Thanks. Trip report & other pictures eventually.