CHIANG RAI – Recent findings from Rocket Media Lab show arsenic-contaminated water is now a risk in not just the Kok River but also the Sai and Ruak rivers. Agriculture in these areas faces further losses, possibly adding 547 million baht in damages.
Heavy metals and arsenic are turning up in rivers that cross from Myanmar into Chiang Rai, putting the province’s farm economy under real pressure. It’s now clear that not just the Kok, but the Sai and Ruak rivers are unsafe, with contaminated water threatening more than 63,000 rai of farmland and pushing expected losses much higher.
On 17 September 2025, Rocket Media Lab published data on communities along the Sai and Ruak rivers. These findings help estimate the economic costs if the contamination continues to halt farm activities that rely on river water.
Water checks between 23 and 27 June 2025 confirm arsenic levels exceed safety standards not only in the Kok River but also in the Sai and Ruak, which run through Mae Sai and Chiang Saen districts. Every check revealed unsafe readings.
Five sub-districts affected by the flow of the Sai and Ruak rivers include Mae Sai, Wiang Phang Kham, Ko Chang, Wiang, and Si Don Mun. The rivers stretch over 46 kilometres through these areas, where at least 45,000 people live. Most rely on farming and use river water daily.
Farming Faces Huge Economic Losses
Figures from the Ministry of Agriculture and Cooperatives state that 63,024 rai in these five sub-districts are used for cash crops. The largest is rice, grown on 44,740 rai or roughly 71 percent of the land. Maize covers about 11,500 rai, or 18 percent. Other crops include:
- Rubber: 2,456 rai (3.9 percent)
- Pineapple: 1,687 rai (2.7 percent)
- Cassava: 903 rai (1.4 percent)
- Oil palm: 903 rai (1.4 percent)
- Other fruit (longan, mangosteen, coconut, rambutan, coffee, lychee, mulberry): 823 rai (1.3 percent)
Based on average crop yield and 2024 farm prices, the farmland near the Sai and Ruak rivers generates around 547 million baht a year. This is about 2.2 percent of Chiang Rai’s total farm output. All of this is at risk from toxic water.
Rice is the most exposed crop, making up about 364 million baht or 67 percent of the area’s total farm value. Many rice fields sit next to these rivers and draw water directly for irrigation.
Chiang Rai is one of Thailand’s top rice-growing provinces. In 2024, the main season saw planting across 1.24 million rai with over 677,000 tonnes harvested. Off-season rice also covered 365,000 rai, yielding 357,000 tonnes.
While services lead Chiang Rai’s economy (71.3 billion baht from a total of 107.3 billion in 2022), farming is the second-largest sector at 25 billion baht (about 23 percent). Industry ranks third, valued at 8 billion baht.
Fishing and Aquaculture Also Impacted in Chiang Rai
Water contamination is hurting more than crops. Those who fish or raise fish in these rivers also face real hardship. In 2024, freshwater fishing in Chiang Rai yielded 1,417 tonnes worth over 92 million baht, mostly tilapia and common carp. Within the five affected sub-districts are 284 fish farms, covering nearly 690 rai. A prolonged crisis could deal a crippling blow to these operations.
Previous research from Rocket Media Lab found that contamination in the Kok River alone could cause farm sector losses of 3.24 billion baht across 16 sub-districts, close to 13 percent of the province’s total farm value.
Adding the new 547 million baht in losses from the Sai and Ruak rivers brings the total potential loss across all three rivers to 3.78 billion baht per year, around 15 percent of the farm sector’s value. The total farmland at risk includes 63,000-plus rai along the Sai and Ruak, and over 340,000 rai by the Kok, bringing the total affected area past 400,000 rai.
This pollution crisis has dragged on for more than six months. It started when villagers in Tha Ton, Mae Ai district, Chiang Mai, noticed that water in the Kok looked odd and could no longer be used for drinking or daily life.
Tests confirmed the Kok River contained arsenic and heavy metals above safe levels. The contamination comes from rare earth mining upstream in Myanmar. Since then, regular tests have found more sites with worrying levels along all three rivers.
What makes this hard to fix is that the source of pollution lies in Myanmar, beyond the reach of Thai environmental controls. Yet it’s Thai farmers and families who feel the effects.
The combined economic threat from contaminated water in the Kok, Sai, and Ruak rivers underscores the need for joint action to deal with cross-border environmental problems that keep harming local people. Future risks cannot be ignored and should be met with clear, coordinated plans.
