Heavy metals and toxics, much of it from Shenzhen, is altering the food chain
Water pollution in Deep Bay has caused changes in migratory bird species at the Mai Po wetland by killing off the food of some birds while encouraging the growth of food favoured by others, conservationists say.
Crabs were dying in the contaminated waters while worms, snails and algae were thriving, said the local chapter of the global conservation body WWF, which manages the nature reserve.
The green group yesterday urged a joint working group of the Hong Kong and Shenzhen governments to disclose water quality data from the Shenzhen side of the bay, as pollution remained unchanged despite a big reduction in the discharge of effluent by Hong Kong.
WWF Mai Po reserve officer Bena Smith said Hong Kong discharged 13.4 tonnes of effluent a day into Deep Bay in 2005, a 40 per cent decrease from 1996. But he said water quality remained poor and this was reflected in the changing species of water birds at Mai Po.
One species that has increased significantly in recent years is the pied avocet, a winter migratory bird. Fewer than 1,000 were recorded in 1990, but this increased to more than 8,000 last year.
On the other hand, the number of Saunder's gulls has fallen from 170 in 1990 to 50 last year. The gull is classified as vulnerable with only 3,000 recorded worldwide.
