Blue Holes
A New Jersey "Blue Hole" is a sand quarry that has filled with water from the aquifer below. These are very dangerous places. This is because, although the visible part may look like a Caribbean beach, the underwater sides of the quarry are steep and unstable, and merely walking near the edge can cause a collapse into the hole. The water is deep and cold, and the victim is quickly overcome by shock and hypothermia and drowns.
I have marked a few of the bigger and more notorious Blue Holes that might look like good places to go on a satellite image. They are not. Most Blue Holes are either state-owned or private property, and strictly illegal (and stupid) to trespass.
