By 
Worawan Klinsawai
Md Arafat Ul Alam, February 5, 2023
In early April 2025, hazardous contaminants were detected in water samples from Kok and Sai Rivers in Northern Thailand. Local authorities warned the residents to refrain from direct use and consumption of river water, while experts and activists called for government discussions between Thailand and Myanmar to find solutions and regulate mining activities.
In early April 2025, the test results of water samples from Kok and Sai rivers in Northern Thailand revealed excessive amounts of heavy metal contamination, including arsenic, lead, and cadmium. Local authorities in Chiang Mai and Chiang Rai issued public warnings, advising residents to avoid direct use or consumption of the river water. As both rivers flow from water sources shared between Thailand and Myanmar, experts and activists pressured the Thai Government to urgently discuss the solutions with the Myanmar counterpart and relevant ethnic groups.
The pollution was suspected to have derived from mining activities for gold, manganese, and zinc by Chinese companies in Shan State, Myanmar. Since 2020, Chinese investors have expanded their mining operations upstream of the Kok and Sai rivers. These mines were alleged to release water used in the metal extraction processes into the rivers without adequate water waste treatment.
Arsenic contamination levels were the most concerning. The safety standard of arsenic in river water is set at 0.01 milligram per litre (mg/L). However, water samples from Kok River contained arsenic levels of 0.026 mg/L, twice as high as the threshold. 0.014 mg/L of arsenic was also detected in the samples from the Sai River.
The hazardous residues can cause rashes and diarrhoea, while long-term exposure can lead to serious health problems such as cancer. With rising concerns, Thai authorities will continue testing water samples collected from different spots in Northern Thailand and encourage cooperation from Myanmar.
Sources and Further Readings:
Arsenic, lead in Kok River causes alarm
Experts call for Myanmar talks over Thai river contamination
Arsenic Linked to Chinese Gold Mines Found in Chiang Rai’s Sai River
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