China's top environment agency has sent investigators to probe a chemical company's dumping of carcinogenic industrial chemicals into a reservoir that feeds one of the country's largest rivers.

Investigators from the Ministry of Environmental Protection arrived at Qujing in southwestern Yunnan Province Thursday, the city government's information office said.

They will investigate the pollution of the Chachong Reservoir in the town of Yuezhen and the Nanpan River which feeds into the Pearl River, a major river that flows through southern China.

Luliang Chemical Industry Co., Ltd., which was found to have illegally dumped over 5,000 metric tons of chromium-contaminated waste near the Chachong Reservoir and in hills of Luliang county in Qujing from April to June, suspended production on Sunday.

"Rainfall in June washed some of the chemicals into local water supplies and caused 77 cattle to die," the Pearl River Water Conservancy Committee said on its website Thursday.

The committee, which is under Ministry of Water Resources and joined the investigation early this week, has found excessive cancer-causing hexavalent chromium (chromium VI) at the company's dumping sites.

The committee said no apparent chromium VI pollution was detected in major drinking water sources, including the Huangnipu Reservoir and the Nanpan River.

No human deaths have been attributed to the chromium pollution, but at least 14 local residents have been diagnosed with cancer since 2002 and many suspect their diseases were caused by contaminated drinking water.

At least 3,000 people live near the company's dumping sites.