An artificial reef off Koh Racha Yai, Thailand, popular with divers, were coated in cement 2 weeks ago, reported phuketwan.com.

A mass reef clean-up involving 20 volunteer divers, conservation staff and local sea gypsies, was said to take place the following Friday and Saturday, to save the reef by dusting off the corals coated with cement.

The spill was caused by a barge transporting building materials to a construction site of a new hotel in Siam Bay. The barge ran into trouble when it started taking on water during heavy swells.

The copious amounts of water quickly soaked cement bags, which made the barge unstable and, at the order of the captain, several bags of cement were jettisoned to try and stablise the boat. The barge was right above the artificial reef at the time.

The Phuket office of Marine Coastal Resources Conservation was alerted by hotels and diving companies. Upon investigating the site, bags of cement were discovered littered around the reef, with up to 10 ruptured bags releasing cement powder.

Some corals on the artificial reef were already dying under a crust of hardened cement. Natural coral reefs in the area, the closest one being 30m away, were not damaged in the incident.

The artificial reef was established in 2005, to alleviate environmental pressure on the natural reef from the tsunami and give it a chance to recover.

The barge owner, Namchai Sea Transportation Co., has agreed to pay for the cleanup cost.