I had a snapping turtle grab hold of my stringer of fish last year. I thought I snagged up on something, untill I gave my stringer a good pull and up came the turtle hanging onto one of my fish. I cut the fish off with my knife and I headed into shore. What a surprise.
I know this may sound unsporty, but I know of a section of water in the Shenango River where fish become trapped in the summer months when the water level drops down. Fishing is good there most of the time.