The Pine Barrens area of New Jersey has plenty of small lakes or ponds that people call “blue holes”. Because of the legends surrounding them, they have become quite popular. The Pine Barrens are coastal pinelands where the soil is sandy, acidic, and nutrient-poor. That means the land isn’t good for much but it supports a valuable ecosystem. The holes are spring-fed and usually do not freeze in the winter.
The most famous Blue Hole is in Winslow, NJ. near the Great Egg Harbor River that eventually empties into Great Egg Harbor. According to this article from 2003 in the South Jersey Courier-Post paper, this was a haunted and treacherous spot called Beelzebub’s bottomless pit and the Jersey Devil’s bathtub. Typically, water that flows or collects in this area is the color of tea, tinted by the tannins of the cedars. But the blue hole was said to be blue. It’s not anymore but it can be clearer than other water because it’s spring-fed and still. The cold temperature from the upwelling water means less active bacteria that could turn it brown.
Like many other local lakes, people thought it was bottomless and tried to plumb it but were not successful. Kids were warned not to swim in it because the water was so cold. Stories developed that it was inhabited by demons that tried to drown swimmers.
The true blue hole is small. I noticed on Google earth that someone labeled an old water-filled sand and gravel pit as a blue hole. The water here is turquoise blue because of the chemistry (could be high or low pH and has mineral content that causes the color to appear blue). This artificial water body is not the traditional “blue hole” but it likely still is cold and dangerous to swim in because of the loose sand and possibly submerged objects. The real blue hole is north of this pit.
More: Legends and science of bottomless pits, bogs and lakes