State executive councillor Hee Loy Sian said the contamination was prevented and cleared through biological treatment in a mere five hours by the Selangor Water Management Authority (Luas).

“The contaminated water flow had the potential of affecting the operations of the state’s four water treatment plants,” he said in a statement, adding that the water treatment plants accounted for 60% of water supply to Selangor, Kuala Lumpur and Putrajaya.

Hee said the blue-coloured water was traced to a factory at the Integrated Industrial Park in Rawang. It had flowed out of the factory’s drains to Sungai Gong, a tributary of Sungai Sembah and Sungai Selangor.

Sungai Selangor is the Klang Valley’s primary source of raw water.

He said a polluted patch was detected at 1am at Sungai Gong today and “code yellow” was activated, with immediate bio-remediation treatment put in place.

Hee said by 6am, the affected waterway, located some 500m away from the factory, was restored to normal.

He said the factory spewing out the liquid had been ordered to stop work and to shut off its final discharge point. He added that the factory was also being investigated under the Selangor Water Management Authority Enactment.