Thailand and Myanmar sign water quality pact amid persistent arsenic contamination
A cross-border agreement signed in August 2026 has created a new joint mechanism to monitor water quality in rivers shared by Thailand and Myanmar, as contamination from unregulated mining continues to affect communities in northern Thailand.
The Thailand Pollution Control Department and Myanmar's environmental authorities signed a Terms of Reference agreement valid for three years, establishing a framework for data exchange and coordinated monitoring of border rivers.
However, civil society organisations and experts have raised concerns that the agreement focuses on monitoring rather than addressing the source of pollution. Myanmar's amendments to the original draft removed provisions requiring joint investigation reports and pollution source mapping, replacing them with a narrower requirement to identify only risk areas.
Arsenic levels exceed safety standards
The Mekong River Commission reported in July 2025 that arsenic concentrations exceeded the 0.01 milligram per litre standard at four of five sampling sites along the Kok and Mekong rivers, classifying the pollution as a "moderately severe" environmental problem.
Thailand's monitoring in February and March 2026 found ongoing contamination in the Kok, Sai, Ruak and Mekong rivers. Sediment testing yielded more alarming results than water samples, with concentrations exceeding Thailand's danger threshold for benthic organisms.
Researchers from Chiang Mai University found the highest contamination point at the Golden Triangle, where readings reached 296 milligrams per kilogram in sediment — far above safe levels for aquatic life.
Research from Mae Fah Luang University in February 2026 detected arsenic accumulation in hair and nail samples from residents in four sub-districts along the Kok River, indicating the heavy metal has built up in bodies faster than it can be eliminated.
Impact on farmers and fishers
Agricultural communities in Chiang Rai province report declining yields, with rice plants producing abnormal shrivelled grains and farmland soil turning white and cloudy after floodwaters recede. Some farmers who previously had contracts to sell crops like sweet corn lost their buyers due to safety concerns.
Fish populations have declined significantly, with fishers catching deformed fish showing signs of disease — heavy metals damage immune systems in fish, making them unsellable. Some riverside residents stopped eating fish and vegetables from the river entirely.
The contamination source lies in unregulated rare earth and gold mines in Myanmar's Shan State, often reported to be backed by Chinese investors. Myanmar's government denied the existence of such mines at the headwaters of the Kok River in a letter to the United Nations on 17 June 2026.
Regional cooperation expands
Beyond the bilateral Myanmar agreement, Thailand and Laos signed a Memorandum of Understanding in May 2026 on consistent regulations for safe navigation and pollution prevention in the Mekong.
The Thai cabinet approved a new environmental cooperation MoU with Laos in August 2026, extending coverage to air, water and soil pollution, climate change and disaster response. This agreement is scheduled for signing in September 2026.
The Mekong River Commission approved its draft strategic plan for 2026–2030 in September 2025, aiming to strengthen monitoring tools and expand cooperation with upstream countries.
Yet the Commission's authority remains limited over key upstream areas in Myanmar and China, meaning pollution from beyond member state borders falls outside its jurisdiction.
Calls for stronger action
Civil society groups continue to push for Thailand to take a leading role in negotiating joint standards at the sub-regional level, including demands to:
• Declare affected areas disaster zones
• Establish health surveillance programmes
• Push for an end to mining at pollution sources
• Create a local water quality testing centre in Chiang Rai
Without stronger enforcement mechanisms and source-country cooperation, the monitoring framework signed in August offers improved data exchange but limited power to stop contamination at its origin.
