Dean's Blue Hole, Blue hole in Long Island, Bahamas

Dean's Blue Hole is a circular opening in the seafloor near the coast of Long Island in the Bahamas, extending over 200 meters down into underwater limestone. The round surface opening measures roughly 30 meters across and drops vertically into a maze of caverns and passages below.

When sea levels dropped during ice ages, rainwater dissolved the limestone layers and carved deep shafts in the dry rock. After sea levels rose again, the system flooded with salt water and formed this formation.

The name comes from the dark blue circle visible against the turquoise shallows. Since 2010 the Vertical Blue freediving competition has been held here, organised by William Trubridge, who opened a freediving school on Long Island. During the contest, AIDA judges and safety divers are on site, and competitors including Herbert Nitsch and Alenka Artnik have set records in the hole.

A narrow path over rocks leads down to the beach and entry point into the water. Snorkeling and swimming gear are helpful since the depth increases quickly and visibility along the edge of the hole often stays clear.

Around 20 meters down, the narrow shaft widens into an enormous chamber roughly 100 meters across. The side walls suddenly disappear and divers float in open space above an abyss that continues deeper into darkness.