The factories will not be allowed to operate again until they meet environmental protection standards, said Ding Haizhong, Communist Party of China secretary of the city.

The public informed officials earlier that the Cihu River was being seriously polluted. The river is located to the north of Ma'anshan and is an important water source of the city.

The city government investigated the complaints and found the pollution primarily came from the mines and chemical plants on the upper reach of the Cihu.

The pollution discharged by the factories has affected the safety of portable water and water used for irrigation, Ding said.

The pollution in China's longest river, the Yangtze, has worsened over the last ten years as billions of tons of waste continue to be dumped into China's "mother river".

A report made by Yangtze River Water Resources Commission shows that 30 billion tons of polluted water were dumped into the river last year, 50 percent more than in 1998.

About 27.5 percent of the river's water is so seriously polluted it can not be treated to be made potable, said the report. The percentage in 1998 was below 20.

China has reported more than 150 major water pollution cases so far this year.