The environmental group said it analysed 25 samples of wastewater discharge from several industrial sites and found a "diverse range of hazardous chemicals," including heavy metals associated with causing brain damage.

"What is very disturbing is that, once released, it is almost impossible to remove these hazardous substances from the environment," said Kevin Brigden, a scientist at the group's research laboratories.

The river -- China's third-longest -- and its surrounding area will suffer irreversible damage if the government doesn't impose strict environmental regulations on the manufacturing heartland, Greenpeace said.

Local companies should also cut their use of hazardous chemicals, the report said.

"'Made in China' products used by consumers worldwide are being manufactured at a high cost to the Pearl River," said Edward Chan, campaign manager for Greenpeace China.

"If the results of our sampling are any indication of what factories in general are doing in China, then China's waters are in deep trouble."

Critics have also called for a clamp down on air pollution from the region's factories, which has been blamed for covering nearby cities, including Hong Kong, with a blanket of smog.

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