The national environmental watchdog has started a probe into the alleged illegal discharge of untreated sewage and toxic waste into a river and lake in Xinyu city, Jiangxi province.

The Ministry of Environmental Protection said on Thursday that it suspects Yichun Zhong'an Industrial Co, a chemical plant, discharged the pollutants on April 3.

The waste that spewed into the Yuanhe River, which links to Xiannyu Lake, contained toxic chemicals including arsenic, thallium and cadmium.

The lake is the city's water source.

The city immediately stopped using water from the contaminated lake and only resumed on April 10, the ministry said.

The city switched to using backup water sources from other regions to guarantee a stable supply for residents. Monitoring of the contaminated lake now shows water quality is back to acceptable levels, it said.

Now, the ministry wants to find out what happened and who was responsible.

The incident happened after the chemical plant was ordered to suspend production in March, the provincial environmental authority said. The plant is believed to have illegally continued to produce chemical products and waste products.

It is suspected of disposing of waste through a 2.5 kilometer hidden pipe, the provincial environmental watchdog said.

Waste in the pipe was found to have alarmingly high levels of poisonous cadmium - 46,550 times the national safety standards - it said.

The authorities have sealed the factory and removed the sewage pipe.

zhengjinran@chinadaily.com.cn