The Environment Department of Selangor has discovered that the illegal activity of a premises cleaning used metal drums believed to contain chemical wastes is the cause of Sungai Aur in Klang turning blue.

Selangor DOE director Nor Aziah Jaafar said an operation conducted together with the Klang Municipal Council enforcement unit and the police, which ended at 8pm yesterday, resulted in them coming across hundreds of used drums.

"We discovered hundreds of used drums...