LANTAU environmentalists have accused a government department of treachery over the future of an area of outstanding natural beauty. The 60-strong Green Lantau Association (GLA) is furious that proposals for a works area look set to go ahead in the island's most scenic valley. The Water Supplies Department has applied to develop part of the Wong Lung Valley on Lantau's north side while construction of a reservoir is carried out nearby. The group said that the site was given Countryside Conservation status by the government. The GLA fears that because the application stresses the development will only be temporary, it will definitely get the go-ahead - even though ''temporary'' means up to five years in Hong Kong planning terms. Wong Lung, which means yellow dragon, nestles between some of Hong Kong's highest peaks and is home to the rare barking deer, the slipper and butterfly orchids, ancient woodland, kites and kingfishers. It borders North Lantau Country Park and is one of the island's most isolated spots. The Water Supplies Department had been dumping rubble and other waste there until earlier this year. Following complaints from the GLA they stopped, cleaned the site, erected fencing and carried out some re-seeding. However, after a change of staff at the department, they have now formally applied to the Island Districts Land Office to use part of the valley as a works area. A spokesman for the Water Supplies Department said the land would be used as a site office for contractors during the building of a the reservoir to cater for the airport at Chek Lap Kok and a new town nearby. The GLA fears the department will resume more rubbish tipping at the site and wants it to find somewhere else less environmentally sensitive for the development. ''This proposal is against stated planning intentions,'' Fabian Pedrazzini of the GLA said. ''Because the application is for temporary use, we won't be entitled to object. That's wrong. It allows them to by-pass the normal consultation process. ''This valley, with its Countryside Conservation status, should be a buffer between developed areas and fully protected areas like the country park. ''We are interested to see if the Government sticks by its commitment to protecting conservation areas. ''The Water Supplies Department were dumping here before we intervened so we suspect they'll dump here again. Once they get their hands on the site they can extend the use of it many times. People's enjoyment of the area will be massively restricted.'' A spokesman for the Island Districts Lands Office confirmed an application had been put forward for development of a works area. He said it would be considered by all government departments. He confirmed that because the application was for temporary use, there would be no public consultation. He said that this was ''standard procedure'', although no decision on the application had yet been made.