Authorities in the eastern city of Nanjing are investigating reports that factories along China's Yangtze River have been dumping toxic effluent into the water there, following action by local residents.
Seven factories near Lianmeng village in Nanjing's Qixia district were pumping out large quantities of pollutants into the river water, the Yangtze Evening News quoted local residents as saying.
Villagers had manipulated local pumps and drainage systems to divert the water away from their commercial fish farms, and directly into the Yangtze River, the paper said.
"To test the level of pollution, they bought two large, healthy Crucian carp and put them in a tank full of the polluted water," the paper said.
"In less than 10 minutes, both fish were floating dead on top of the water."
An official who answered the phone at the Qixia district environmental protection bureau said officials were investigating the allegations.
"The environmental protection bureau is at the scene, dealing with this incident," the official said.
"We aren't all assigned to this one incident; we have a specialist team that monitors illegal polluting incidents, and they are all at the scene right now," he said.
"But if you want to know what's going on, you should contact our propaganda department; their entire purpose is to disseminate information."
Calls to the Lianmeng village committee went unanswered during office hours on Thursday.
Local sources later said that the environmental teams had "found no pollutants" at the scene, however.
Nanjing-based environmental activist Liu Guanghua said pollution in the Yangtze was already known to be very serious.
"It's not just the chemical factories emptying waste there," Liu said. "Our tests have shown in the past few years that toxic effluent sometimes pours into the Yangtze from the Qinhuai River sluice-gates."
"As soon as they open the sluice-gate from the Qinhuai River, all the fish in the Yangtze River die off," he said. "Downstream of this, there are two intake pipes for a treatment plant for Nanjing's tap water."
"I have photos as evidence that all the fish die when they release the water."
Liu said he and his fellow activists had repeatedly brought up the issue with the authorities, but to no avail.
More than three decades of breakneck economic growth have taken their toll on the country's natural resources, sparking a huge increase in public unrest linked to environmental degradation and health problems caused by pollution.
Activists who confront the authorities and vested commercial interests over pollution are often subject to revenge attacks and government harassment, however.
Authorities in the eastern province of Jiangsu on Wednesday sentenced environmentalist Ji Shulong two two years' imprisonment for "obstructing official duty," and "stirring up trouble and picking quarrels," her relatives said.
"This is simply revenge on the part of the police," Ji's nephew Ji Jianjun told RFA's Cantonese Service, who said the charges against his aunt were trumped up.
Officials have admitted that China is facing a "grave" environmental crisis, with more than half its cities affected by acid rain and one-sixth of its major rivers too polluted even to water crops with.
Tap water supplied to millions of residents in hundreds of Chinese cities routinely fails to pass water quality tests, official figures show.
According to a January report from the State Environmental Protection Agency and the Chinese Academy of Engineering, around 90 percent of the water table under China's major cities is polluted to some extent, with residents of the worst-affected areas forced to buy drinking water.
Reported by Fang Yuan for RFA's Mandarin service and by Lin Jing for the Cantonese service. Translated and written in English by Luisetta Mudie.