Toxic contamination in upper stretch of Mekong River “moderately serious”: MRC

The latest assessment also shows arsenic was also detected along the Lao-Myanmar border, hinting at possible sources beyond national boundaries, said the MRC

The Mekong River Commission (MRC) is conducting an assessment of the water quality of the Mekong River in the upper stretch encompassing the Thai-Myanmar-Lao border and has found that the arsenic level was beyond the standard limit set at 0.01 mg/L.

The latest attempt by the regional water diplomacy body to govern the use of the river is to try to address concerns over water quality in the Mekong’s tributaries, including the Kok River flowing from Myanmar’s Shan State under the Wa armed group’s influence and passing through Thailand’s Chiang Mai and Chiang Rai provinces before joining the Mekong.

The assessment conducted by the organisation revealed that four out of five sampling sites had arsenic concentrations above the standard limit of 0.01 mg/L. The upstream at Houa Khong and C1, as well as downstream at Luang Prabang, showed arsenic levels below the threshold. The contamination was detected from C2 to C5, which implies that the contamination is likely entering the river between C1 and C5. No lead was detected in the Mekong River stretch within the Lao PDR.

When compared with the May 2025 assessment by Thailand’s Pollution Control Department (PCD), arsenic levels in the Mekong remained consistent at around 0.025 mg/L. Arsenic was also detected along the Lao-Myanmar border, hinting at possible sources beyond national boundaries.

l Locations of CRMN-WQMN stations: Houa Khong (LHK) and Luang Prabang (LLP)/ Location of 5 sampling points in Bokeo, Lao PDR. Credit: MRC

Based on the findings, the MRC has classified the situation of the water quality of the river as a “moderately serious” under the MRC’s Technical Guidelines for Water Quality Emergency Response and Management. It has notified the potentially affected countries.

The organisation will hold a meeting and field visit later this month in Chiang Rai to try to advance its proposal for joint water quality monitoring among the three countries. A road map for future collaboration will also be developed, with the MRC Secretariat facilitating the exchange of ideas and technical inputs.

“The MRC remains committed to supporting its Member Countries and Dialogue Partners in promoting data sharing, regional cooperation, and the joint management of transboundary water resources to ensure a healthier Mekong Basin,” the organisation noted.

The MRC started to engage in the issue as there has been a public outcry over the water quality of the Kok River and a few others in the same area, as well as the Mekong following extensive mining in the Shan State under the Wa armed group’s influence near the Thai-Myanmar border.

In late April, the Thai National Mekong Committee (TNMC) formally requested the MRC to help engage Myanmar, which is a Dialogue Partner under the MRC framework, to jointly assess this emerging issue. In response, the MRC Secretariat’s Environmental Management Division promptly initiated coordination efforts to facilitate a collaborative approach.

It proposed the establishment of a Joint Water Quality Monitoring (JWQM) initiative between Myanmar and Thailand. According to the MRC, the initiative aims to enable a scientifically grounded assessment of the water quality and promote coordinated action. 

It is anchored in the Procedures for Water Quality (PWQ), one of the MRC’s five core procedures agreed upon by its four member countries, which includes regionally agreed-upon Water Quality guidelines for the protection of human health and aquatic ecosystems. The PWQ also provides a mechanism for assessing and communicating incidents that may have potential transboundary impacts.

The initiative will cover the exchange of data, technical expertise and resources between the environmental agencies of both countries. Its key work components will include regular water sampling and analysis at critical locations along the Kok River, joint capacity-building activities, the development of early warning systems for pollution events, and transparent public reporting to engage local stakeholders and communities.

Myanmar officially responded to the proposal, expressing its willingness to participate in the joint monitoring initiative, the MRC said. 

Also read: Myanmar responds to MRC’s initiative to address water quality in Kok River/ Thai Govt plans to talk with Myanmar to address toxic contamination in Kok and Sai Rivers in the North