A diving teacher has backed down on her claims about a diving site in Phangnga suffering severe damage by what she described as dynamite fishing that caused a large number of aquatic animals to die.

Thon Thamrongnawasawat, a lecturer with Kasetsart University's faculty of fisheries, on Saturday posted on his Facebook page an apology by the diving teacher whose previous Facebook post had prompted an inspection of the diving site known as Richelieu Rock at Mu Koh Surin National Park.

Richelieu Rock is known as one of the world's top 10 diving sites.

The apology, written in English and taken from a Facebook page with the user name Aey Payackapan, reads: "Guys, I have to apologise for the big misunderstanding about Richelieu Rock.

"Many people have been investigating and there seems to be no evidence of an explosion.

"The fish could have been dead by many reasons, so it was wrong of me to assume it was an explosion.

"Richelieu is still beautiful and full of life and I apologise for giving wrong information."

Along with the message from the diving teacher, Mr Thon also posted an explanation given by the head of the national park to improve the public understanding about the diving site being mistakenly thought to have been damaged.

Previously, the diving teacher stated on her Facebook page that Richelieu Rock had been devastated by dynamite fishing, claiming that close to a million large and small aquatic animals had been wiped out in a powerful explosion.

On Friday, Nattapol Rattanaphan, chief of the marine national park division, denied the explosion had occurred. The department has also arranged for guards to take care of it 24 hours a day.

He maintained that park officials usually went on patrol to take care of the Rock, which is regarded as one of the country's most important diving sites.

Previously, there was a report of an explosion killing fish nearby the site, which was reported to be an act of trawlers from a neighbouring country.

Mr Thon said the fish might have been killed by illegal fishing tools.