Works reduce key stream to just a trickle
The only waterway on Hong Kong Island to be included in a list of ecologically important streams has been narrowed to the width of a drain by anti-mosquito works carried out by the government.
Boulders from the bed of the stream in Deep Water Bay Valley - home to two species of rare freshwater fish - have been moved to the banks, where vegetation has been cleared by the Food and Environmental Hygiene Department.
Chong Dee-hwa, president of the Ichthyological Society of Hong Kong, said such a complete stream in good condition was hard to find on Hong Kong Island. 'It is really needless [to remove the boulders]. When the stream is altered a little bit, the loss could be immeasurable.'
The stream is one of 33 'ecologically important streams' identified by the Agriculture, Fisheries and Conservation Department.
Yiu Vor, a butterfly researcher who visited the area on Sunday, said about 1.3 kilometres of the channel had been disturbed. 'I saw some department's contractors moving boulders to the bank a few years ago at the lower stream. When I asked, the workers said they were carrying out anti-mosquito work,' he said.
Two workers at a nearby golf course and a hiker who frequented the valley all said they saw government work being carried out in the stream several times a month.
A Food and Environmental Hygiene Department spokesman confirmed it had been regularly carrying out anti-mosquito work in the stream to prevent the anopheles mosquito, which spreads malaria, from breeding. He said the mosquito breeds in unpolluted streams with slow water flow and vegetation on its banks.
'Obstacles' and plants slowing the water flow were removed, he said. Staff work within guidelines to ensure the ecology is protected as mosquitoes are destroyed, but the department will talk to the Agriculture, Fisheries and Conservation Department to follow up the works, he said.
Chong said it was a 'completely wrong concept' to think there were mosquitoes in moving water. He said they only breed in stagnant water.
The stream, which runs from Wong Nai Chung Gap to Deep Water Bay, is a mix of salt and fresh water. Watermarks on the bank show that the water was once half a metre deep and the stream six metres wide.
But with boulders piled up on the banks, the stream was now as narrow as half a metre. Chong said boulders served as shelters for many fish and could slow the water flow. Their removal damaged habitats, and cutting vegetation could also hurt the food chain and cause landslides. 'Now water is being drained quickly to the sea ... in the worst case, the whole stream may disappear,' he said.
Yiu said thousands of milkweed butterflies had been seen in the valley every winter since 2003. But this winter, for the first time, there were none. He also said he had not seen any Pygoluciola qingyu, a firefly once found in the valley, for several months.
Alan Leung Sze-lun, conservation manager of WWF Hong Kong, said a 2001 study found the stream was home to two species of rare freshwater fish - Stiphodon and Schistura. No fish were seen there yesterday.
The stream's upper section is within the boundary of a site of special scientific interest in Deep Water Bay, which is recognised for its biodiversity of butterflies and rare plants, including Seaside Dutchman's Pipe, a shrub. Many trees were seen chopped down on the nearby slope and stream bank. Some tree trunks - with diameters as large as 45 centimetres - lay on the ground.
An Agriculture, Fisheries and Conservation Department spokeswoman said it would visit the site and liaise with other departments to find out more about the situation.
