Today I was by the C&O Canal in Georgetown, Washington, D.C. where the canal begins (or ends, depending on which way one is traveling). Here is a view of the canal from M Street.
Notice the abundant tracks in the mud in the canal.
I suspect they are turtle tracks. I couldn't get closer to them to take a better look, but this particular track on partially dried mud had what appeared to be feet marks on each side.
I can't think of any other animal that would have left a track like that. Curiously, even though I walked along the canal for more than an hour towards Georgetown, I didn't see any turtles.