Deepest blue hole (sinkhole)
Last updated: October 14, 2017 at 1:47 am
Dragon Hole, 300 m (987 ft), Paracel Islands, South China Sea (a.k.a. the Eye of the South China Sea) – At least 20 species of fish have been observed above 100 m (328 ft) depth. The blue hole is largely devoid of oxygen—and life—beyond 100 m (328 ft).
Dean’s Blue Hole, 202 m (663 ft), Long Island, Bahamas – A blue hole is a steep vertical cave or sinkhole filled with different layers of water. Water circulation is poor therefore little life is found in its depths. Blue holes are nonetheless connected to the sea through fissures or branches.
Black holes are land-based versions of blue holes. The water in a black hole is virtually stagnant and thus contains large amounts of bacteria and dangerously high levels of acidity. Diving in a black hole is extremely dangerous.