The Pollution Control Department (PCD) has reported a rise in arsenic levels in the Kok, Sai and Mekong rivers during its latest round of monitoring in February, while noting high turbidity in some areas and advising residents to treat water before use.
In a statement released on March 20, 2026, the PCD under the Ministry of Natural Resources and Environment said it had conducted its 16th round of water and sediment quality monitoring between Feb 24–27, 2026, covering the Kok River and its tributaries, as well as the Sai, Ruak and Mekong rivers in Chiang Mai and Chiang Rai provinces.
Overall, most heavy metals remained within national surface water quality standards. However, arsenic concentrations exceeded the standard level of 0.01 milligrams per litre in several locations.
In the Kok River, elevated arsenic levels were recorded at four monitoring points, from Tha Ton Bridge in Chiang Mai to a crossing in Doi Hang, Chiang Rai, with concentrations ranging from 0.013–0.016 mg/litre.
In the Sai River, arsenic exceeded standards at all monitoring sites, with levels between 0.011–0.015 mg/litre.
In the Mekong River, exceedances were detected near the Golden Triangle permanent border checkpoint and at a Provincial Waterworks Authority intake in Mae Sai, with values between 0.014–0.015 mg/litre.
The Ruak River remained within standard limits at all monitoring points.
The PCD said it would continue close and ongoing monitoring and regularly update the public. It also advised residents who need to use river water to ensure proper treatment before consumption or use to reduce health risks.
An accompanying analysis noted that since March 2025, continuous monitoring has shown the rivers to have a light brown colour with high turbidity in some areas. While most heavy metals remain within acceptable limits, arsenic continues to exceed standards in parts of the Kok, Sai and Mekong rivers.
For comparison, results from the 15th round of testing showed that arsenic levels in the Kok River were largely within standards except for a stretch near Tha Ton, while the Sai River consistently exceeded limits. The Ruak and Mekong rivers were previously within acceptable levels.
Meanwhile, local authorities and tourism agencies are preparing to host the “Three Lands Songkran Festival” in Chiang Saen from April 13–18, featuring activities such as a 250-metre water tunnel, cross-border cultural parades and boat races along the Mekong River.
This is a translation of original Thai news article https://transbordernews.in.th/home/?p=45485