Chinese divers Denovo Xu and Sun Hao failed to surface from an exploratory dive on 6 September.

They were visiting a deep underwater section of the wall that passes through Panjiakou Reservoir in Hebei province, a three-hour drive from Beijing,

Search teams from the nearby city of Tangshan and from Beijing have continued to search for the divers with the help of remote cameras and sonar scanning.

Their disappearance was reported in The Beijinger by Steven Schwankert, the founder of dive operation SinoScuba, who has written about diving in China for Diver.

The Great Wall of China was constructed in stages between the 8th century BC and the 17th century AD, but the underwater section was formed 40 years ago, when a river was dammed and the reservoir created to boost water supplies to Tangshan and Tianjin.

Several hundred metres of the wall were flooded in the process and the shallower section is now said to be popular with leisure divers, but the area in which the divers went missing would have been deeper than 40m and only rarely visited

Technical divers face “the challenges of cold water, especially at great depths, and often limited visibility,” says Schwankert.

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