Environmental protection officers are investigating claims that contaminated stream water flowing from a construction site for the MTR's high-speed railway killed more than 2,000 fish in a Yuen Long village last week.
The dead variegated carp, worth about HK$100,000, were raised by a villager in a pond filled with water pumped from the stream - said to be as alkaline as an ammonia solution.
Residents of Yau Tam Mei Tsuen - known for the breeding of aquarium fish - demonstrated to the officers and media yesterday how a few sample fish died in the grey, muddy stream water in 30 minutes.
They say they now fear more fish will die and are worried about the effects on their own health.
"Some villagers are worried that they may get poisoned someday just like the fish," said Lo San-cheung, a member of the villagers' concern group.
Officials from the Environmental Protection Department collected several water samples from the stream running from the site where the underground railway's Ngau Tai Mei to Tai Kong Po tunnels are being built.
Preliminary tests showed that the water samples were relatively alkaline, and detailed reports would be available after two weeks, the department said.
A villager who used a pH meter to measure the level of acidity and alkalinity in the stream near the pond and the site found a reading of 11.2 at both locations, meaning the water samples were as alkaline as ammonia solution.
"The water is too alkaline for raising fish," said Dr Paul Shin Kam-shing of City University's department of biology and chemistry. "The fish may have died of suffocation as the highly alkaline water harms their respiratory systems."
The villagers said explosions at the site contaminated the underground water, which was discharged into the stream.
The 26-kilometre Hong Kong section of the high-speed railway running from Kowloon to the boundary of the city and Shenzhen will be connected to the mainland's railway network.
The MTR Corp said the site's contractor was granted a licence by the government for sewage discharge in accordance with the Water Pollution Control Ordinance. It said the contractor had taken various measures, including filtering, before discharging the water.