Hard to discern the exact design shown. Petroglyphs afford us an insight into the minds of the ancients. Many times they represent clan symbols. Other times hunting scenes and game animals, some probably designed to promote hunting "magic" or success. Oft times shamanic figures are shown in transformative states, half human, half animal for instance. Where there is one, there will likely be more, so keep your eyes peeled for sure.
Here is a photo taken at the Mark Rock petroglyph site on Narragansett Bay, RI. Years ago, I used an old map of the site, determined the scale used, and hit a bullseye in finding this double water petroglyph. The site is almost entirely buried at this point. Sign of the Water Clan? Who can say at this point in time.