Dean's Blue Hole

Dean's Blue Hole is the world's deepest blue hole (underwater sinkhole), which plunges 202 metres (663 ft) to the ocean floor, in a bay west of Clarence Town on Long Island, Bahamas . . .

In April 2007, William Trubridge broke a free-diving world record in the blue hole reaching a depth of 84 metres (276 ft) without the use of fins. In April 2008, during the Vertical Blue 2008 free-diving competition, a total of 25 national records and 5 world records were broken. During this event, William Trubridge broke his own world record in the Constant Weight Without Fins (CNF) category reaching 86 metres (282 ft) as well as breaking the record in Free Immersion (FIM) at 108 metres (354 ft). In April 2009, Australian Walter Steyn achieved a new Australian free-diving record of 100 metres (330 ft) at Dean's Blue Hole.

Blue holes are the results of rainwater having soaked through fractures of limestone bedrock onto the watertable of glacial sea levels during the Pleistocene epoch (ice age), some 15,000 years ago. The maximum depth of other known blue holes and sinkholes is 110 metres (360 ft), which makes the 202 metres (663 ft) depth of Dean's Blue Hole quite exceptional.

Dean's Blue Hole is roughly circular at the surface, with a diameter ranging from 25 to 35 metres (82–110 ft). After descending 20 metres (66 ft), the hole widens considerably into a cavern with a diameter of 100 metres (330 ft).