Pollution Alert for 'Kok River' and 'Sai River' – Arsenic Levels Exceed Standards, Avoid Direct Use

The Pollution Control Department (PCD) has issued an urgent warning regarding the water quality in the northern region, specifically for 'Kok River' and 'Sai River,' where arsenic levels have exceeded the safety standards. The public is advised to refrain from using the water directly. Meanwhile, 'tributaries, Ruak River, and Mekong River' remain safe.

Today (February 14, 2026), the Pollution Control Department (PCD) of the Ministry of Natural Resources and Environment reported on the ongoing monitoring of water quality and sediment in the Kok River, its tributaries, Sai River, Ruak River, and Mekong River, covering Chiang Mai and Chiang Rai provinces. The monitoring aims to mitigate the impact of ongoing contamination and turbidity concerns in the water sources.

The 15th water quality analysis, conducted from January 13-16, 2026, found that most heavy metals, including cadmium, copper, nickel, chromium, zinc, and mercury, were within the acceptable limits. However, arsenic levels exceeding the standard (more than 0.01 milligrams per liter) were detected in some areas, as follows:

Kok River: Arsenic levels exceeded the standard between the Tha Ton Bridge in Mae Ai District, Chiang Mai, and the Mithraphap Bridge at the border of Mae Vang-Tha Ton in Chiang Mai, ranging from 0.011 - 0.012 milligrams per liter. Other areas in the KokRiver were within the safety standards.

Tributary Rivers (Fang River, Korn River, Lao River): Arsenic and other heavy metals in all monitoring points were found to be within the safety standards.

Sai River: Arsenic levels were still above the standard in all monitoring locations, with average levels ranging from 0.011 - 0.014 milligrams per liter.

Ruak River: Water quality has returned to normal, with arsenic, lead, and copper levels at all monitoring points within the standards.

Mekong River: In Chiang Rai province, arsenic and other heavy metal levels were found to be within the safety limits at all monitoring points.

The ongoing monitoring, which has been in place since March 2025, indicates that water quality changes according to seasonal factors. During periods of heavy rainfall or flooding, the higher water flow may help dilute contaminants in certain areas. However, upstream areas near pollution sources continue to face risks from accumulated contamination.

The Pollution Control Department (PCD) will continue to monitor water quality closely and update the public regularly. It is recommended that residents in the affected areas avoid using water from highly turbid natural water sources directly for consumption or other uses. If necessary, the water should undergo purification processes or be sourced from a certified water supply system to ensure health safety.

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