It is a worm's worst nightmare: the mudflats of Mai Po are rising in a slow but inexorable process that has rung alarm bells among scientists and conservationists. Together with inner Deep Bay and the fishponds, Mai Po marshes nature reserve is the most important wetland in southern China, providing a vital staging post for migratory birds en route to their breeding and wintering grounds. But swirling mud disturbed in Deep Bay is washing up on the mudflats, pushing a greater expanse above the high-tide mark. It may represent only three centimetres in a decade but more mud means dramatic changes to the mudflat ecology. Worms and crabs are not the only ones turned off by the influx of stinking gunge. Their predators, the gulls and waders which refuel on the rich pickings during their Mai Po pit-stop, also seem to be suffering. One of the largest protected wetlands in southern China, Mai Po is an avian oasis in a sea of development but its lifeblood, Deep Bay, is being poisoned. For 15 years the number of birds flocking to Mai Po has increased annually, but last year they declined for the first time by nearly 4,000. This year's winter water-fowl count brought cold comfort: 10,000 fewer birds than the previous winter, a 19 per cent drop from the peak of 1996 when numbers reached 68,000. Warning signs first emerged in June 1996 when the usual mid-summer explosion of benthic organisms on the mudflats - 'wall to wall crabs' - did not happen. 'There were virtually no crabs,' says executive director of the World Wide Fund for Nature (WWF) Hong Kong, David Melville. Compared with 1988-89, mudskippers had declined tenfold. Conservationists sighed with relief when things improved the following year although the density of mudskippers, crabs and worms did not compare with past years. And then the bird numbers began to decline. 'It is very worrying,' says Dr Lew Young, manager of Mai Po. WWF is the first to admit the annual bird census - when teams of ornithologists stake out inner Deep Bay - is not scientific. This year strong winds and foggy weather may have partly accounted for the low numbers, Dr Young says. But even taking that into account, says Alex Yau, a WWF senior conservation officer, 'it is a sure sign of warning'. She adds: 'A 19 per cent decrease over two years is pretty significant. It is definitely a cause for concern.' The dynamics of Deep Bay are complex and not easily understood, says Dr Young. He points to two phenomena at work: worsening water quality and increasing sedimentation. One of Hong Kong's most polluted water bodies, contamination in Deep Bay reached a nadir in 1996 - the worst of the previous eight years - with unprecedented levels of ammonia and low dissolved oxygen at the height of summer. Environmental Protection Department officials deny the pollution was from Hong Kong. Rising mudflats are a different matter, caused by silt being churned up in Deep Bay by massive earth-moving on the northern shore on the mainland. A natural process determined by the hydrology of the bay, the effects have been magnified by infrastructure projects on the mainland, according to Dr Young. It was not until 1995, when conservationists chanced upon satellite photographs of the northern shore of Deep Bay and Futian Nature Reserve, that they had any idea about what was happening. Futian Nature Reserve is half the size it was and its mangroves, which once hugged the coastline, have been wiped out by the Binghai causeway, a road linking Shekou port and Shenzhen. On the silted up land behind the causeway there are plans for hotels, commercial buildings and a science park. The development will fill in 20 per cent of inner Deep Bay. When chairman of the Advisory Council on the Environment (ACE), Peter Wong, visited Futian in December, he was shocked by the scale of development. 'It is a construction site. It really was like Chek Lap Kok. It was amazing,' recalls Ms Yau. Nature reserve officials were amused by the wide-eyed visitors from across the border. 'They were surprised at how surprised we were.' Talk to Hong Kong officials about the causeway and more recent extension of Shekou port, and the shutters come down. 'We keep asking what is happening - we seem to have better information than they do,' Mr Wong says. 'All government officials are a little too polite to ask in case they stir up a real hornet's nest. We are very early on in our SAR days and nobody really knows how to handle it.' Greater co-operation is essential to the health of Mai Po, says Mr Wong, but past experience does not bode well. 'When you are dealing with the Shenzhen government which allows 600 hectares of Futian reserve to be taken over by development of one sort or the other and it requires a state council directive to mark out the boundaries, how much co-operation can you expect?' Cross-border communication has reached such an impasse, says Mr Wong, it is now beyond the scope of the Hong Kong Guangdong Environmental Protection Liaison Group and should be taken up by the chief secretary and governor of Guangdong. For WWF, requests for monitoring data about the ecological status of Deep Bay from cross-border projects like the Shenzhen River Regulation have become a frustrating exercise. In 1996, the Government told the ACE that the monitoring programme for the project had concluded that 'no catastrophic phenomena had been observed'. Six months after a request for more detailed information, WWF took matters into its own hands and visited Shenzhen to see their data. 'Now we have returned to the motherland - but we are still not part of it,' says Ms Yau, leaning on a file centimetres-thick with fruitless correspondence. 'It's considered to be a state secret.' However, a spokesman for Planning, Environment and Lands Bureau denied any impasse. The joint working group set up to monitor the environmental aspects of the Shenzhen River had access to the data and 'reported regularly to ACE', he says. 'The project had not caused any adverse impact on the surrounding area.' On the Binghai causeway, officials on the technical sub-group of the Hong Kong Guangdong Environmental Protection Liaison Group had 'expressed concern and asked about the progress' - but only in November 1995, months after conservationists had learned of the project. Not only is accessing cross-border data like pulling teeth, complain conservationists, but the cumulative impact of individual projects is also ignored, leaving them wondering what grim surprises to expect next. Managing Mai Po in the 21st century was never going to be easy, despite its long awaited designation in 1995 as a Ramsar site - or wetland of international importance. Under siege on all fronts, at risk are Mai Po's major claims to ornithological fame: the Dalmatian pelican, and the black-faced spoonbill - a globally endangered species numbering only 450 worldwide, some 27 per cent of which spend the winter at Mai Po. That alone would qualify it for Ramsar status, but the 1,500-hectare site boasts 13 other regionally important species and more than 20 rare kinds of invertebrate. Those birds unable to refuel at Mai Po because of insufficient food might lack the strength to reach their distant breeding and wintering grounds and die en route. The Agriculture and Fisheries Department, responsible for the Ramsar site, is planning a long-term ecological monitoring programme to better understand the situation. 'As the decline appears only in the recent survey, it is too early to say that it is a real decline or is just a natural fluctuation over the years,' a spokesman says. Despite obligations under the Ramsar Convention, the department's spokesman says at this stage 'we do not see the need to inform the Ramsar Convention secretariat' about the ecological changes at Mai Po. 'I disagree,' says regional co-ordinator, Asia, of the Ramsar Bureau, Rebecca D'Cruz from her office in Gland, Switzerland. 'Because going by the rules in terms of obligation, if there is a classic case of potential change in ecological character, in other words that means deteriorating quality of the site, then that is definitely something they should be informing us about. It is an obligation they have undertaken.' Ramsar sites in Asia are few and deserve close attention, particularly Mai Po. 'Mai Po is one of the leading success stories so it is especially interesting to us and of great concern if it is the case,' she says. A precautionary approach is best, agrees Peter Wong, even if the scientific proof of decline is unavailable. 'One has to be concerned whether this is the beginning of a downward trend. No-one would wish to be pilloried in later life as the person who allowed Mai Po to be destroyed.'