Blue HoleOffshore flooded caves, so-called ocean blue holes, are extensions of the sea, subject to the same heavy tides and host to many of the same species found in the surrounding waters. Inland blue holes, however, are unlike any other environment on Earth, thanks largely to their geology and water chemistry.
Fresh WaterIn these flooded caves, such as Stargate on Andros Island, the reduced tidal flow results in a sharp stratification of water chemistry. A thin lens of fresh water—supplied by rainfall—lies atop a denser layer of salt water. The freshwater lens acts as a lid, isolating the salt water from atmospheric oxygen and inhibiting bacteria from causing organic matter to decay. Bacteria in the zone just below the fresh water survive by exploiting sulfate (one of the salts in the water), generating hydrogen sulfide as a by-product. Known on land as swamp or sewer gas, hydrogen sulfide in higher doses can cause delirium and death.
Dive Blue HolesAs living laboratories, inland blue holes are the scientific equivalent of Tut's tomb. From a diver's perspective, they're on par with Everest or K2, requiring highly specialized training, equipment, and experience. Even more than high-altitude mountaineers, cave divers work under tremendous time pressure. When something goes wrong, if they don't solve the problem and make it back to the cave entrance before their gas runs out, they're doomed. - Andrew Todhunter, National Geographic, August 2010
A blue hole is a sinkhole in which deep saltwater layers are covered by surface fresh water. The underwater caves can be found across the islands of the Bahamas. Blue holes are roughly circular, steep-walled depressions, and so named for the dramatic contrast between the dark blue, deep waters of their depths and the lighter blue of the shallows around them.
Dean's Blue HoleThe deepest blue hole in the world is Dean’s Blue Hole. This most famous blue hole is 663 deep and can be found in a bay west of Clarence Town, Long Island.
For the best blue hole exploration in The Bahamas you will want to visit Andros or Long Island where local business feature blue hole dives.