Who is stealing sand from our beaches? The question, raised by a nature lover on the letters page of Sunday's South China Morning Post, has sparked an investigation by the Agriculture, Fisheries and Conservation Department. It will probe whether illegal dredgers have made off with sand from three beaches and a sand bar, as suspected by physics teacher Stephen Woo Yan-chuen. Mr Woo told the Post that he suspected illegal dredging on Kat O Island (Crooked Island), Wong Wan Chau (Double Island) and in Sai Kung East Country Park, based on trips he made to the sites over the past eight months. He said there was once a 20-metre-long white sand bank at the southwestern tip of Kat O Island but it had disappeared when he visited the site earlier this month. Last October, he was shocked during his trip to Wong Wan Chau when he discovered huge sections of orange-golden sand had been dug away on Tung Wan Beach, leaving a series of large pits and ditches on the beach. He also reported that fine white sand apparently had been dug away from Tai Long Tung Wan and Tai Long Tai Wan in Sai Kung Country Park when he visited there last August. Any dredging at the locations would be illegal. The physics teacher expressed shock that such beautiful natural sights had been damaged. He said it was unlikely that such large volumes of sand could be washed away by natural causes. But it was possible that mainland sand bandits had sneaked into Hong Kong waters to carry out the illegal dredging, he said. A government source said the sand could have been dug away by local villagers to help provide concrete for houses in remote areas. Yesterday, the Agriculture, Fisheries and Conservation Department promised to investigate.