Chung's study surveyed and observed 80 divers at seven popular diving spots near Sai Kung and found that each person touched coral 14.7 times on average in each dive. The majority of those were inexperienced or carrying cameras, and contact was unintentional and mostly caused by their hands and fins.

"It's difficult to stay still in the water, so when a photographer needs something to hold onto, coral may become the victim," said Chung, who has been diving for 10 years. "It's a myth that diving won't affect marine ecology."

Chung found nearly 40 per cent of divers said they made contact with coral because they lost control of their buoyancy; 8.6 per cent said they were taking pictures; and 6.2 per cent just found the coral convenient to hold on to.

The study showed that camera-carrying divers made contact an average of 23.8 times per dive, compared with 11.6 times for others. It counted 81 damaged coral colonies in the seven spots, of which 19 were in the Sharp Island area, 18 near Shelter Island, 16 off Bluff Island and 13 in Long Ke.

Chung said novice divers should practise buoyancy control in swimming pools or less ecologically sensitive areas before going to other spots, and all divers should be vigilant when they were underwater.

"They could … check whether water became murky where they were. In that way, they would know whether they were kicking up sand and adjust their finning and kicking," she said.

Chung suggested that restricted areas be set up in popular and sensitive spots such as Sharp Island and Hoi Ha, and bans be imposed on divers and snorkellers until the coral could recover.

"In Hoi Ha, the water is very shallow and some people even walk on the coral with their sneakers on," she said. "Although some coral can recover by itself after time, for some, the damage is irreversible," she said.