In a statement posted on its official Facebook page, the DoE said its industrial enforcement unit, which conducted the investigation, found that the river water was indeed black and emitted  a foul odour as stated in the public complaint.

It said department officers had obtained details of the incident from nearby residents to facilitate the investigation.

According to the DoE, a team from its Pasir Gudang branch had also scoured the river area on Thursday and monitoring by drone was carried out to identify the cause of the pollution.

“River water quality assessments have also been carried out by the monitoring unit of Johor DoE at several locations along the river.

“Preliminary investigations found that the pollution was suspected to be caused by the disposal of wastewater from non-industrial premises which carried out maintenance work, causing untreated wastewater to flow into a nearby river,” it said.

It added the premises involved were asked to carry out immediate repair measures and the local authority had been informed to take further action.

According to the DoE’s statement, sampling was also conducted and sent to the Chemistry Department for further action under the Environmental Quality Act 1974.