Authorities in southern China are trying to protect Guangzhou and other densely populated cities from a toxic spill flowing downriver toward municipal water intakes.

A zinc smelter dumped wastewater heavily contaminated with cadmium into the Bei River a week ago.  Chinese news media say the river is now carrying up to 10 times more cadmium than is considered safe.

The city of Yingde, up stream from Guangzhou, has already stopped drawing water from the Bei River.

Authorities in Guangzhou say emergency measures to safeguard drinking water are under way.  Chinese news reports say reservoirs have released large quantities of stored water to dilute pollution in the river.

Cadmium, a metal used in several manufacturing processes, is highly toxic and can cause serious neurological, kidney and liver ailments. 

The contamination of the Bei River is China's second major environmental incident in recent weeks.