Dragon Hole is the deepest known underwater sinkhole (blue hole) in the world. It is 300.89 metres (987.2 ft) deep. and is located about 25 kilometres (16 mi) south of Discovery Reef in the Paracel Islands at Coordinates: . Blue holes are characteristically hundreds of metres deep and generate a distinctive blue colour when seen from above.
Dragon Hole is almost 100 metres (330 ft) deeper than Dean's Blue Hole in the Bahamas. There are several fresh water sinkholes on land that are deeper than Dragon Hole. These include Mexico's Zacatón (335 metres (1,099 ft)), Pozzo del Merro in Italy (392 metres (1,286 ft)), and Hranice abyss in the Czech republic (404 metres (1,325 ft)).
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