BEIJING >> Residents and water plants along a river in southern China that is used as a drinking source have been warned not to use the river’s water after authorities detected excessive amounts of two dangerous chemicals.

Tests by authorities detected the chemicals thallium and cadmium in a section of the Hejiang River in Guangdong province after dead fish turned up in the water, the official Xinhua News Agency said today.

The Fengkai county government warned downstream water plants and residents against using the water or eating anything from the river, Xinhua said. Cadmium is considered an environmental hazard, and thallium is extremely toxic. No illnesses have been reported.

Xinhua said the pollutants were believed to have come from upstream, and later reports said excessive amounts of the chemicals were detected in the upstream Guangxi region. The reports didn’t say how the pollutants got into the stream.

Hejiang is a major tributary of the Xijiang River, which serves as the primary water source for Macau and the city of Zhuhai.

Water pollution is a serious problem in China due to unscrupulous industrial waste disposal.