China's second largest freshwater lake, Dongting Lake, has been tested clear of contamination from discharges of toxic arsenide less than 20 kilometers upstream into a tributary.
The lake's water quality had been unaffected by the contamination of the Xinqiang River in the central Hunan Province, sources with the State Administration of Environmental Protection said on Monday.
Environmental protection authorities of the province and the county are monitoring the water quality of the lake, a major drinking water source for Hunan.
The county government has increased water discharges from two reservoirs on the upper reaches of the river to help dilute the pollution.
Local government officials anticipated the drinking water supply from the river for residents in the county would likely be resumed on Tuesday.
No casualties have been reported from the contamination in Yueyang County since its drinking water source was found polluted on Friday when workers from the county's environmental monitoring center conducted routine testing of water quality and found the content of arsenide was 10 times higher than normal standard.
The incident has drawn the attention of the State Council, China's cabinet, and local governments.
The provincial government initiated an emergency plan for dealing with environmental accidents, while a base to handle the accident was set up in the county with a population of 100,000.
Local authorities issued warnings to residents against drinking tap water and sent fire engines to distribute drinking water to the people.
The cause of the accident was ascertained as illegal discharges of industrial sewage by three chemical plants upriver in Linxiang City.
Environmental experts say arsenic trioxide is a highly toxic white powdery substance that can cause vomiting, stomach pains and convulsions, and can lead to coma or death.
A chronic intake of arsenide can also cause liver and kidney damage or lung and skin cancer.