An unscrupulous contractor tips tonnes of construction rubble into a wetland used by migratory birds in Yuen Long A marsh used by migratory birds in Kam Tin is at risk of being destroyed by an unscrupulous contractor who dumped tonnes of construction waste on the site. The privately owned site is in Au Tau, Yuen Long, which birdwatchers say is a popular wetland habitat for migratory birds. The site was the focus of concern by green groups and birdwatchers several years ago, when they revealed that contractors on the West Rail project had been dumping waste there. On Monday, a birdwatcher saw at least 23 trucks unloading waste at the site over two hours. Subsequent investigation yesterday found that all the trucks came from a construction site near Pok Oi Hospital that is being supervised by the Drainage Services Department. The drainage project is being carried out by contractor Sun Fook Kong. Tipped off by birdwatchers, the department yesterday immediately ordered the contractor to stop transporting waste from the site. It is not known how long the ban will remain. 'We have issued a strong warning to the contractor,' a department spokesman said. 'We might also take disciplinary action against them by suspending their qualification to bid for our new projects for a period of time.' Under an environmental permit issued to the contractor, the trucks are required to dump the waste in landfills or two Yuen Long construction sites that can use it. The spokesman believed the trucks loaded with rubble left the original construction site through unauthorised exits and dumped it in the marsh. Measures to prevent such use of the unauthorised exits are being worked out. However, Mike Kilburn, vice-chairman of the Hong Kong Birdwatching Society, suspected the dumping was an organised activity related to the demand for small houses. 'Some of the indigenous villagers might deliberately want to spoil the marsh by paying the drivers to dump waste there' to make way for building sites, he said. Mr Kilburn said the incident had exposed flaws in conservation policy because similar incidents had taken place in Shuen Wan, Lam Tsuen and Sha Po. 'It is an obvious sign of the failures of the conservation policy, and the new policy under review raises nothing to address the threats facing these freshwater habitats.' He said such dumping threatened to drive away migratory birds, including the rare grey-headed lapwing and the painted snipe. A consultation document by the Environment, Transport and Works Bureau aims to conserve privately owned sites with high ecological value that are under constant threat of development. Cheng Luk-ki, conservation head of the environmental group Green Power, said it was not uncommon to discover dumping breaches in Yuen Long. 'Drivers who want to make more money might be tempted to dump waste in a place close to their construction site and are reluctant to go further to dump the waste in landfill or public fill sites,' he said. He warned that an increasing number of property developments and water-channelling works in the region meant more remote sites would fall prey to illegal dumping.