Deep-hulled boats are regularly taking visitors into shallow waters at Hoi Ha Wan Operators of glass-bottomed boats have been threatened with prosecution and warned to stay away from shallow marine park waters after divers found damaged coral in the areas where they give tours. Government officials have also expressed their 'grave concern' to operators of one 30-metre glass-bottomed boat, named after Hoi Ha Wan, which has been taking visitors around the coral in the bay. At least three glass-bottomed boats have been running tours into coral-rich Hoi Ha Wan this summer, cashing in on the delay in the launch of the World Wide Fund for Nature Hong Kong's (WWF) own glass-bottomed boat, possibly until next year. The WWF vessel is specially built to travel in coral areas without damaging corals. Touted as Hong Kong's first glass-bottomed boat, it was due to go into service this year but has been held up by the delayed opening of the Hoi Ha Marine Life Centre, where it is moored. The rival glass-bottomed boats, run by self-styled eco-tourism companies, are modified sampans with deep hulls, which environmentalists and the Agriculture, Fisheries and Conservation Department fear may damage corals in shallow areas. The boats are believed to have had their glass bottoms added on mainland, and one operator is believed to have a 90-seat vessel - twice the size of some existing boats. Undercover marine officers have joined the tours and found they visit shallow coral areas. Subsequent checks on corals found signs of damage caused by 'a large and heavy object', although it has not yet been proved that the boats are responsible. A fisheries spokesman said of the coral damage: 'We are still collecting evidence for the purpose of enforcement action. We are also considering imposing statutory controls over this kind of coral-viewing activity in marine parks.' Talks have been held with operators and a prohibition zone was set up on June 1 restricting entry of large vessels - such as the 30-metre Hoi Ha Wan - to shallow coral areas in the marine park, he said. 'We have expressed our grave concern to the operator over the possible damage this vessel could inflict on coral in shallow waters,' the spokesman said. 'We will continue to monitor the operation of glass-bottomed boats including sending undercover officers on board and collecting information and evidence for the purpose of prosecution, if the situation warrants.' The fisheries department's tough stand comes after both the WWF and the Friends of Hoi Ha group called for action against the glass-bottomed boat operators, warning they were putting both the corals and swimmers at risk. Environment consultant Paul Hodgson, who has worked with the WWF on some of its Hoi Ha projects, said: 'These are vessels with deep hulls. Their propellers are not designed to be used around divers and they are operating in very shallow water. We have had close encounters already.' He suspected the boats probably were damaging corals, especially when fibreglass vessels now carrying 30 to 40 people ventured into water only one metre deep. He said the boats, most of which set out from Tai Po, were putting their own livelihoods at stake if they failed to take sufficient care of the corals in Hoi Ha Wan.