Huang Youping has depended on the Longjiang River to earn a living for more than 20 years. But on Jan 7 the stock in his fish farm floated to the surface. "At first I thought it was just bad luck."

Then his neighbors reported that their fish stocks were also dead. Huang realized that something must be wrong with the water.

Huang, 42, lives in Desheng town, Yizhou city, in South China's Guangxi Zhuang autonomous region. On Jan 15 the authorities told Huang and others that tests showed cadmium contamination. Cadmium is a carcinogenic heavy metal used in manufacturing batteries and paints and if ingested by humans can be fatal. It softens bones and causes kidney failure.

There is no known medical cure for cadmium poisoning.

Experts estimate that 20 tons of cadmium leaked into the Longjiang, polluting up to 300 kilometers of the river. Its peak concentration was 80 times the allowable limit.

Downstream, Liuzhou city scrambled to neutralize the chemical spill and its threat to tap water for more than 3.5 million people.

Initial investigations show that lack of pollution treatment, illegal discharging of toxic sewage, and poor supervision by local authorities are causes of the chemical spill.

Nine people have been detained on suspicion they were responsible for the contamination, and local authorities say the river water is now safe. But people who live next to the river and make their livings from it aren't sure.

A villager checks stocks in his fish farm in Yizhou, South China's Guangxi Zhuang autonomous region, on Wednesday. Cadmium leaked from a factory into the Longjiang River where his fish farm is located. Jiang Dong / China Daily