He said the latest incident took place yesterday, involving an oil spill in a river in Kampung Baru Balakong. But, he added, probes by relevant agencies found that it did not come from any factory or workshop around the area.

“Three days ago, we detected the same type of pollution in Sungai Kundang, Rawang. I’m concerned that this was purposely done but I have no proof.

“I urge all parties including those who were negligent, please … this could affect millions of residents due to disrupted water supply,” he told reporters here today.

Amirudin said the state government had recently increased the number of enforcement officers and personnel to monitor river basins in the state to avoid contamination from recurring and that they would be equipped with drones from Sunday onwards.

Earlier, Selangor Water Management Authority (LUAS) in a statement said it received a complaint from members of the public at about 6pm yesterday on a pollution incident in Kampung Baru Balakong, and the investigation found that it was caused by used engine oil being dumped at the location.

It said the contaminated water would have entered Sungai Balak and Sungai Langat but LUAS had placed oil pads and booms at the scene to prevent the oil from flowing into the rivers.

It added that the investigation also found that the affected location was a stagnant water area and it was suspected that the oil dumping was done by a third party.