A woman has described the terrifying moment when she saw a huge shark as she swam with a group of children off Lamma Island. Police confirmed the presence of a shark yesterday and authorities ordered the closure of 12 beaches on Lamma and Hong Kong Islands. Anne-Sophie Girard was on a catamaran yacht, moored off Sham Wan, and enjoying a party with her husband Martin, their four children, aged five to 12, and friends when she took a dip yesterday afternoon. But summer fun turned to horror when the boat's captain spotted a fin and ordered the 15 swimmers, including Girard and her two youngest children, back onboard. 'At that moment we were just really scared. It was quite a big shark. It was a close call,' she said. The couple believe the creature they saw was a whale shark, the world's largest shark species, due to distinctive markings on its back. 'It is very big, grey with white dots on it, and its fin is black,' Girard's husband said. Despite their alarm, the couple say the creature did not appear aggressive, even as it swam under the yacht. Whale sharks feed mostly on plankton and are not considered a significant threat. A sighting of a shark about four to five metres long was reported to police at about 1pm yesterday, about an hour before the Girards' ordeal. Police patrol vessels confirmed the shark's presence and the Leisure and Cultural Services Department quickly raised red closure flags on beaches. A marine biologist played down fears the shark could threaten participants in the Dragon Boat Carnival, starting in Victoria Harbour today. 'The chances of a shark coming into Victoria Harbour would be very low. They would usually appear in clean waters following the ocean currents in summer. In Hong Kong, sightings are mostly reported in eastern and southern waters,' said Dr Samuel Hung Ka-yiu, the Hong Kong Dolphin Conservation Society chairman.