KUALA LUMPUR: Sungai Buah in Nilai which flows into Sungai Semenyih is still contaminated with a highly poisonous substance, 4-Bromo Diphenyl Ether, forcing the Selangor government to disrupt water supply for the third time this month.

"It is highly poisonous and that is why dead fish were found floating nearby," said Elizabeth Wong, executive councillor for tourism, environment, green technology and consumer affairs.

She said the contamination posed a serious health threat and the source of the contamination was a drainage system in Sungai Buah in Nilai, Negri Sembilan which flowed into Sungai Semenyih.

"It is not the smell that is the only concern but the pollutant which is causing it.

"Analysis by the Selangor Water Management Board (Luas) identified the substance as 4-Bromo Diphenyl Ether,” Wong told reporters after attending a Special Chambers proceedings in Parliament here.

She said water samples taken from Sungai Buah still emit a strong smell which had to be diluted four times for it to be odour free while water at the source of contamination in Nilai had to be diluted 20 times.

Wong said the pollutant is suspected to have been deliberately dumped into the drainage system near the Elite Highway.

She said the Selangor government had requested the Department of Environment (DOE) in Negri Sembilan to pump out the contaminated water from the river there and store it in bunds.

"The water is not to be used but will be stored at the bunds and treated with enzymes," she said.

Wong said Luas lodged a police report last Sunday on alleged sabotage of the water supply and handed over a sample of the water to the federal DOE.

The Sungai Semenyih Water Treatment Plant was forced to close temporarily on several occasions since September following contamination at Sungai Semenyih.

Sources of the pollution had been identified to come from an industrial site in Semenyih, including Sungai Langat, which gets water from Pahang.

The closures caused water disruptions that have affected over a million residents in the Klang Valley.