CHIANG RAI – The Pollution Control Department (PCD), under the Ministry of Natural Resources and Environment, shared results from ongoing checks on heavy metals of water and sediment in key rivers in Chiang Rai.

The monitoring covers the Kok River and its tributaries, plus the Sai River, Ruak River, and the Mekong River across Chiang Mai and Chiang Rai. These inspections continue because unusual turbidity and possible contaminants have been reported over time.

For Round 15, samples collected between January 13 and 16, 2026, were tested against Thailand’s surface water quality standards. Overall, most heavy metals stayed within the standard range, including cadmium, copper, nickel, chromium, zinc, and mercury. However, arsenic still exceeded the standard in some locations (above 0.01 milligrams per liter).

Kok River

Arsenic exceeded the limit from the Tha Ton Bridge in Mae Ai District, Chiang Mai, through to the Nawawang Tha Ton Friendship Bridge in Chiang Mai. Recorded values ranged from 0.011 to 0.012 milligrams per liter. Meanwhile, other Kok River sampling points remained within the standard.

For tributaries (the Fang River, Korn River, and Lao River), arsenic and other heavy metals met the standard at every monitoring point.

Sai River

Arsenic remained above the standard at all monitoring points. Average values ranged from 0.011 to 0.014 milligrams per liter.

Ruak River

Water quality improved and returned to normal conditions. Arsenic, lead, and copper met the standard at all monitoring points.

Mekong River

In Chiang Rai, arsenic and other heavy metals met the standard at every monitoring point.

What the Results Mean and Practical Advice

Pollution Control Department’s continued monitoring since March 2025 shows water quality shifts with the seasons. During high flow periods or heavy rain, increased water volume can help dilute contaminants in some areas. Still, upstream zones near possible pollution sources may face ongoing risk from buildup over time.

The Pollution Control Department will keep tracking water quality closely and will share updates with the public. For safety, people in affected areas should avoid using highly turbid natural water directly for drinking, cooking, or daily use. If water use is unavoidable, it should go through proper treatment or a certified water supply system.

Chinese-Linked Mines Pollute Chiang Rai’s Rivers

People who live along northern Thailand’s rivers are dealing with a growing threat that’s hard to see at first. Heavy metals are turning up in local waterways, and the source points across the border in Myanmar, where mining sites operate with little oversight.

Recent checks by Thai agencies and university researchers found unsafe amounts of arsenic, lead, and other pollutants in the Kok, Sai, and Ruak rivers. These rivers flow into the Mekong River near Chiang Rai, so the problem doesn’t stop at one shoreline.

This spike in pollution ties to a surge in rare earth and gold mining in Myanmar’s Shan and Kachin states. The situation has worsened since early 2025. Many of these mines reportedly connect to Chinese businesses, pushed by global demand for rare earth minerals used in tech and green energy.

Key Rivers Affected and What Testing Shows

Kok River: Runs from Myanmar into Chiang Mai and Chiang Rai. Several samples found arsenic as high as four times the World Health Organization (WHO) limit.
Sai River: Sits along the Chiang Rai border. Tests described it as the most polluted area, with heavy metals above safety levels.
Ruak River: Meets the Mekong. Reports also flagged unsafe arsenic readings.
Mekong mainstream: Tests near the Chiang Rai river junctions found higher arsenic, although levels dropped further downstream in Laos.

Since early 2025, Thailand’s Pollution Control Department has tracked repeated results above safe standards. As a result, officials warned people not to use river water for drinking, bathing, or fishing. At the same time, locals describe orange-yellow water, skin irritation after contact, and “sticky mud” when rain washes runoff into the rivers.

How Communities Are Being Hit

Across parts of Chiang Rai and Chiang Mai, tens of thousands of residents have cut back on river use or stopped altogether. That change has a cost. Local losses tied to fishing, farming, and tourism are estimated at 1.3 billion baht (about $40 million). Fish prices have also fallen because buyers worry about contamination. Even elephant camps have avoided letting animals bathe in the rivers.

For villages near the waterways, including ethnic Lahu communities, daily life has become harder. Water shortages add stress, and long-term exposure raises serious health concerns. Heavy metals can increase cancer risk, harm the nervous system, and affect child development.

Pressure for Action, Plus Real Limits

In June 2025, about 1,500 people gathered in Chiang Rai to push for action from Thailand, Myanmar, and China. Community networks want regular testing, safer backup water supplies, and stronger controls on mineral imports tied to polluted sites.

Meanwhile, the Mekong River Commission has increased monitoring. Still, it has limited power over tributaries inside Myanmar. Research from the Stimson Center highlights the scale of the challenge, reporting more than 2,400 unregulated mines along rivers across mainland Southeast Asia, including hundreds in the Mekong basin.

Experts say this is a clear warning about the costs of the global race for minerals. They also point to the need for tougher cross-border agreements, so pollution upstream doesn’t keep spreading downstream.

As more testing continues, communities in Chiang Rai are staying alert. Many hope that stronger pressure between governments can slow the toxic flow before lasting damage reaches more of the Mekong region.

Heavy Metals in Chiang Rai Rivers Still Exceed Standard Levels