The foul odour affecting Sungai Semenyih has been traced to a palm oil refinery in the district.
Selangor state executive councillor Hee Loy Sian (photo, above) said as such, the refinery has been ordered to cease operations to avoid further contaminating the river.
Other prohibitive measures under Section 121(1) of the Selangor Water Management Authority Enactment are being considered, Hee added.
It is not clear how the refinery contaminated the river or if any fine is being levelled against the operator.
The odour forced a temporary shut down of the Sungai Semenyih water treatment plant last night, affecting water supply to Bandar Puteri, Hospital Serdang, Serdang, Seri Kembangan, Puchong, Technology Park Malaysia, Taman Wawasan, USJ Subang Jaya and UPM.
Hee said activated carbon had been used to combat the odour, which yesterday was measured at a threshold of odour number (TON) seven.
The TON level had gone down to zero as of this morning and water supply is being restored to the affected areas.