A vortexing or non-vortexing circular depression in the water's surface.
Some holes have reportedly appeared suddenly, lasted for a few seconds, and then just as suddenly risen back to the level of the surrounding water.
In the 1990s, three different mariners reported to the Old Sow Whirlpool Survivors Association separate experiences with holes in the water to the south of Cherry Island. In one case, a Deer Island sailboat captain reported suddenly dropping into a hole deep enough that he couldnt see the water's surface. A few seconds later, the hole rapidly vanished, popping the boat back to the surface.
A commercial fisherman reported seeing a hole that he estimated to be 17 feet deep near the same location. Similarly, a tugboat captain reported an earlier experience of looking down about 12 feet into a hole that appeared alongside the vessel while the shaken crew nervously clenched the tugs gunwails.