Its director Ezanni Mat Salleh said the investigation was ongoing, and the samples would be analysed to determine the cause.

“We suspect that mining activities may be involved, but the exact cause will be confirmed once the analysis is completed,” he said, adding that the department is also investigating nearby mining areas located between 19km and 40km from the site.

Ezanni assured that the river’s water quality remains safe and does not pose a risk to local residents.

He said the DoE’s monitoring station in the area had not detected any pollution alerts, and recent monitoring on Oct 9 confirmed the water quality was good.

Ezanni urged the public to report any unusual changes in the water colour or if there were dead fish to assist in the investigation.

Meanwhile, Perak mineral and geoscience department director Nizarulikram Abdul Rahim said their investigation found that the river water had returned to normal the following day, with no evidence of pollution.

The blue water incident was first reported on Oct 21, when a Facebook user shared images of the river turning blue near the Kampung Sungai Papan Bridge, located about 5km north of Kampung Air Ganda, Gerik.