Here are a couple shots (photos by Gary, click to enlarge):
This second photo shows so well the nature of the C&O Canal. As I head upstream along the north (right) bank on the Maryland side, the river is to the left side but just out of sight, with West Virginia across the Potomac River. The towpath, where the mules walked to pull the canal boats, is where you walk/run/bike and is a gravel path.
The actual canal bed, once full of water but now full of trees, is down the embankment to the right. Depth is some 6' to 10'. Further to the right and out of view here would be the other bank of the canal, often a cliff or rock wall.
This shot shows well the river to the left and the towpath in the center. The canal bed to the right is scarcely discernible through the underbrush. In the far distance one can barely make out the beginnings of the area called Four Locks. I'll post some close up shots of the actual locks soon.