So, what are we looking at? This is the confluence of Graham Creek and the Patuxent River.  The main river can be seen in the background. The river is tidal for several more miles beyond this point. Sometimes the tide is so low that the mud flat where silt from the creek settles out of the water before it reaches the river emerges. The tracks were made by a snapping turtle, possibly two.

There is nothing to use as a reference, but the tracks are about a foot across. An average male snapping turtle can reach a width of about fifteen inches. They are extremely cold-tolerant and can be active even under an ice-covered body of water! I have seen one of the snappers that calls this stretch of river home and he is a big one.