Bangkok: Pollution Control Department reveals results of water quality testing round 3, indicating arsenic levels exceeding standards in 11 locations in the Kok River, exceeding all locations in the Sai River and the Mekong River. The turbidity levels are continuously high, suspected to be linked to mining activities on the Myanmar side. Warnings are being issued to refrain from using water and fishing in high-risk areas.
According to Thai News Agency, the Pollution Control Department (PCD), Ministry of Natural Resources and Environment, reported the results of the third water quality inspection of the Kok River between May 12-16, 2025, which found that arsenic (As) was still above the standard at 0.010 milligrams per liter in 11 out of 15 locations in the Kok River, while the Sai and Mekong Rivers were found to have arsenic levels above the standard at every location inspected.
For the Kok River, the points where arsenic levels above the standard were detected included KK01 Thai-Burmese border, Tha Ton Subdistrict, Mae Ai District, Chiang Mai Province, with an arsenic value of 0.030 mg/l; KK02 Mae Na Wang-Tha Ton Friendship Bridge at 0.026 mg/l; KK03 Two Lands Bridge, Ban Mae Salak at 0.018 mg/l; and another 8 points in Muang District, Chiang Rai Province, namely Tambon Doi Hang and Tambon Rob Wiang, where arsenic levels ranged from 0.011-0.018 mg/l. However, the last 3 points, KK13-KK15, did not find arsenic levels exceeding the standard.
In Mae Nam Sai, arsenic levels exceeding the standard were detected at 3 locations: SA01 Ban Hua Fai at 0.023 mg/l; SA02 Friendship Bridge No. 2 at 0.024 mg/l; and SA03 Ban Pa Sang Ngam at 0.017 mg/l.
The Mekong River was found to have arsenic levels exceeding the standard in both locations: NK01 Wiang Subdistrict, Chiang Saen District at 0.026 mg/l, and NK02 Ban Saeo Subdistrict, Chiang Saen District at 0.025 mg/l.
Pollution Control Department analyzed that the points where arsenic levels exceeded the standard were often found in the border areas with Myanmar, especially the Kok River and the upper part of the river, which had abnormally high turbidity levels throughout the river. This is consistent with the characteristics of the area that receives water from the mountains and mining activities on the Myanmar side, especially in the group that pans for ore directly in the river.
For the Mekong River, where arsenic levels were found to be high in some areas, the Pollution Control Department assumes that it was affected by the rivers that meet the Ruak River before flowing into the Mekong River in Chiang Saen District, Chiang Rai Province. Although the water quality of the Kok River through Chiang Rai City has not found heavy metals, the amount of contaminants may still remain in the rivers and the Ruak River, which are directly connected to the Mekong River.
Pollution Control Department warns that areas where arsenic levels exceed the standard may affect public health if water is used without treatment, and may also be harmful to aquatic animals in the ecosystem. Therefore, fishing or water activities in risk areas should not be carried out without clear water quality monitoring.
The tributaries flowing into the Kok River, such as the Fang River, Lao River, Korn River, and Suai River, were also found to have water quality that meets the standard criteria.
The Pollution Control Department has collected water samples for the '4th' quality analysis between May 26-30 and will announce the results immediately once they are received from the laboratory.
Water quality monitoring of the Kok, Sai and Mekong rivers is part of the environmental quality monitoring plan for fiscal year 2025, which is being conducted between March and September. Water samples are collected twice a month and sediment samples are collected once a month to monitor contamination trends and provide ongoing management recommendations.