"Asia’s longest free-flowing river contaminated by arsenic linked to Myanmar mines", 20 Apr 2026, Mongabay

… Independent testing of the Salween River …, when researchers from Thailand’s Institute of Health Sciences Research at Chiang Mai University found alarming levels of contamination detected in the nearby Kok, Sai and Ruak rivers in Chiang Mai and Chiang Rai in Thailand, much of which has been linked to unregulated mining in Myanmar.

In particular, rare earth mines exporting crucial minerals — needed for artificial intelligence, mobile phones, laptops, electric vehicles and renewable energy technologies, among other things — have been blamed. But the mining of gold and various critical minerals also continues largely in secrecy across river basins in Myanmar…

Using satellite imagery analysis, the Stimson Center, a U.S.-based think tank, identified 127 suspected mines operating within the Salween River Basin between 2016 and 2026…

Most suspected mines were found upstream in the Salween’s basin, notably in Shan state, …

… for fishers like Saw Si Paw, much of this information hadn’t reached the community… Residents were aware to varying degrees of the contamination. Few had been given guidance on how to live with the problem. Many had no option but to continue eating fish, drinking water and irrigating crops from the Salween...

… The contamination along Thailand’s rivers was initially discovered nearly a year ago in Chiang Mai province’s Mae Ai district, where mines in Myanmar’s Shan state have contaminated more than 100,000 rai (about 16,000 hectares or 39,500 acres) of farmland with arsenic, cyanide, lead and cadmium.

[...] tests on sediment from the Salween’s riverbed conducted by the Pollution Control Department between Jan. 26 and Jan. 30 found arsenic levels ranging from 36 mg per kilogram to 75 mg/kg across the 13 monitoring points. All exceeded safety standards. Arsenic levels of 10 mg/kg or lower in sediment are deemed safe for benthic organisms while 33 mg/kg is regarded by the authorities as “severely harmful.”

Testing of the river’s water conducted at the same time by the department found arsenic levels ranging from 0.023 mg/l to 0.038 mg/l, nearly four times the safety limit.

Chemicals like cyanide and mercury are often used to dissolve precious metals, separating them from ore, but arsenic and cadmium can be released into ecosystems as mining byproducts. All can cause serious cardiovascular, mental, digestive and reproductive problems, especially after prolonged exposure...

While the Thai communities Mongabay visited had all found some information online, those living across the river in Karen state, Myanmar, were left in the dark.

… Na Paw said he was unaware of mining activity nearby but admitted that information upstream from Shan or Kachin was hard to come by. These two states are, according to local rights groups and satellite imagery analysis by the Stimson Center, Myanmar’s mining hotspots…

Few knew what was safe, and clear information from the Pollution Control Department was absent, in both Thai and Karen languages.

A spokesperson for the Pollution Control Department told Mongabay that the bureau had inspected domestic tributaries flowing into the Salween and “found no heavy metal contamination significantly exceeding the prescribed safety standards.”