We have many non-human visitors to our backyard and last year, one visitor was a snapping turtle. He was making his way to the duckpond next door from one of the reservoirs nearby.
The carapace was 15" in from top to bottom (yes, we did measure it). I can't even guess what it might have weighed. The snapper stopped obligingly while I was taking pictures and although it gave an pretty good "go away" glare, it did not snap even when Pawpa started measuring. When we went back into the house, the turtle continued on it way down to the pond.