Distinguishing silver maple (acer saccharinum, note very small difference in name from acer saccharum, sugar maple) from red maple is difficult, at least before the leaves and fruit emerge. (The leaves will have much more acute lobes, with more dramatic "sinus" openings between the lobes.)

Wojtech mentions the tendency of the silver maple bark to curl away from the trunk somewhat (especially along the sides of vertical strips). I think this makes for some confidence with this particular specimen. Being right at the edge of the river (just above the waterfall) also helps make silver maple a better guess than red maple, though red maple can grow here as well.