About 20 minutes before this photo was taken I watched a juvenile Canadian goose struggle to get free of the grip of this creature (video at https://youtu.be/A8jhQdR4-Cw ). Eventually the gosling got free, but with a severely injured leg. For a while afterwards the turtle lay on its back in the water (see photo #2) and then after thrashing around finally righted itself. Seemed like from head to tail it may have been at least 18 inches long. A not very good video of it flailing in the water can be found here:
https://youtu.be/tR1dntD_3TE