Vientiane, Lao PDR, 20 October 2025 – The Mekong River Commission (MRC) continues to step up its regional response to arsenic contamination detected in the upper reaches of the Mekong River, near its confluences with the Kok and Ruak Rivers in northern Thailand, as recent monitoring results show fluctuating levels of arsenic contamination.

The contamination, first identified in March 2025 in the Kok River, has prompted the MRC Secretariat to coordinate their action with Member Countries in monitoring and mitigating potential cross-border impacts. Acting under its Emergency Water Quality Response and Management framework, the MRC Secretariat has been working closely with Cambodia, Lao PDR, Thailand, and Viet Nam, as well as Myanmar, the MRC’s Dialogue Partner, to strengthen surveillance and share data on the situation.

After being alerted by the Thai National Mekong Committee Secretariat (TNMCS) on 5 April 2025, the MRC Secretariat officially contacted Myanmar’s Environmental Conservation Department (ECD) to propose a Joint Water Quality Monitoring initiative. Since then, several meetings among the ECD, Thailand’s Pollution Control Department (PCD), and TNMCS have been held to exchange information and align monitoring methods.

On 21 July 2025, the MRC Secretariat convened a Regional Meeting in Chiang Rai province, Thailand, to develop a joint monitoring proposal and supported a field visit to the Kok and Mekong Rivers. The meeting aimed to:

  • Clarify the roles and responsibilities of relevant organisations to find appropriate course of actions;
  • Share and review the water quality status of heavy metal contamination in the Kok, Sai, and Mekong Rivers and its possible extent to Lao PDR; and
  • Gather inputs for developing a Joint Water Quality Monitoring proposal and roadmap

The said proposal received strong support from the Member Countries and Myanmar and is now awaiting finalisation for implementation.

Early tests conducted in August 2025 by PCD, with results shared via the TNMCS, indicated that arsenic levels in the Kok, Sai, and Ruak Rivers (Thailand) occasionally exceeded the standard limits of 0.01 mg/L. Although arsenic concentrations at the confluences of the Mekong River with the Kok and Ruak Rivers were within standard limits in August 2025, exceedances were detected in samples collected between 1 and 5 September 2025. Following the reported exceedances, the MRC Secretariat immediately communicated and officially notified Member Countries to remain alert and be prepared for potential transboundary impacts downstream.

In collaboration with the Lao National Mekong Committee Secretariat (LNMCS) and the Natural Resources and Environmental Research Institute (NRERI) of Lao PDR, the MRC Secretariat has been testing water quality at Luang Prabang since June 2025 to assess the extent of arsenic contamination. Current results indicate that arsenic levels have remained below the standard limits from the initial sampling through the latest sampling on 23 September 2025 (see the graph below). In order to strengthen surveillance, new monitoring stations began operating in Bokeo province, Lao PDR, in early October 2025.

To further enhance regional preparedness, the MRC Secretariat is planning regional and national workshops in November and December 2025. These sessions will raise awareness on water quality pollution and strengthen countries’ technical capacity to respond effectively to contamination events. The MRC Secretariat will continue to share updates with Member Countries and the public as new monitoring data become available.

“We understand the concern this has raised among riverine communities,” said Ms. Busadee Santipitaks, Chief Executive Officer of the MRC Secretariat. “This is why our focus is on solid science, close coordination, cooperation, and clear communication. We are watching the situation closely every day and taking action to make sure the rivers are protected, the authorities are involved, and the people are aware.”

About the Mekong River Commission

The MRC is an intergovernmental organisation established in 1995 to boost regional dialogue and cooperation in the Lower Mekong River Basin. Based on the Mekong Agreement among Cambodia, Lao PDR, Thailand, and Viet Nam, the MRC serves as both a regional platform for water diplomacy and a knowledge hub – to manage water resources and support sustainable development of the region.

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For more information, please contact:

Ms. MAO Chandaly
Communications Officer for Press
Mekong River Commission Secretariat
Email: chandaly@mrcmekong.org