For generations, fishing families along the Salween River have drawn drinking water and caught food from one of Southeast Asia’s last major undammed waterways. Now, scientific testing and on-the-ground reporting are converging on a troubling finding: arsenic is showing up in the basin at levels that exceed international safety limits, and expanding, unregulated mining inside Myanmar appears to be making the problem worse.
Peer-reviewed groundwater sampling across central and southern Myanmar, published in the journal Applied Geochemistry by Bacquart and colleagues, detected arsenic concentrations above the World Health Organization’s guideline of 10 micrograms per liter at multiple sites, including areas within the Salween basin. Separately, an Associated Press investigation documented heavy metals, including arsenic, in fish, sediment, and surface water tied to unregulated rare earth mining operations along tributaries in Myanmar and Laos. The AP’s reporting, which included interviews with named Thai officials and researchers, described extraction sites dumping toxins into waterways that feed what the investigation called “the world’s kitchen,” a reference to the region’s vast agricultural and fishing economies.
Together, the two bodies of evidence point to a compounding threat. The Salween runs through geology naturally rich in trace metals, and it passes through territory where rare earth mining has expanded rapidly since 2020. Downstream communities in Myanmar, Thailand, and beyond face a combination of naturally occurring arsenic and industrial pollution that is difficult to untangle on the ground, even when scientists can distinguish the sources in a laboratory.
What the science shows
The strongest data anchor is the Applied Geochemistry study, which used systematic sampling, standardized lab methods, and statistical analysis to establish baseline geochemical conditions across Myanmar’s river basins. The researchers found that arsenic exceeded the WHO’s 10 microgram-per-liter threshold in several groundwater samples, confirming that the region’s geology alone can push contamination into a range associated with serious health risks. Chronic arsenic exposure at these levels has been linked by the WHO to skin lesions, cardiovascular disease, and several forms of cancer.
The AP investigation adds a critical real-world layer. Its reporters visited mining areas, spoke with Thai fisheries officials who described declining catches and discolored water near border rivers, and collected accounts from communities worried about what they were eating and drinking. The investigation focused primarily on Mekong tributaries, but the mining practices it documented, open-pit extraction with no tailings management or wastewater treatment, operate on both sides of the watershed divide. Rare earth mining concessions have proliferated in Myanmar’s Shan and Kayah states, territories the Salween crosses before reaching the Thai border.
Neither source alone proves that a specific mine caused a specific arsenic reading in the Salween. But the pattern they establish is hard to dismiss: arsenic already exists in the basin at concerning levels, and the same type of unregulated mining shown to contaminate neighboring rivers is expanding across the Salween’s own watershed.
Where the evidence runs thin
Important gaps remain. The peer-reviewed study measured groundwater, not the Salween’s surface water. Groundwater and river water interact through seepage, springs, and seasonal flooding, but the relationship varies by location and time of year. No publicly accessible dataset tracks arsenic in the Salween’s main channel with the kind of repeated, multi-year sampling that would reveal whether concentrations are rising alongside mining activity.
The AP documented contamination primarily in Mekong-side tributaries. The Salween and the Mekong share geological traits and are affected by similar extraction methods, but they are distinct systems. Applying findings from one basin to the other requires caution. Researchers have not yet published a study that follows arsenic from a named mining site downstream through the Salween to a population center.
Official data from inside Myanmar is essentially nonexistent. No government agency has confirmed or denied arsenic discharge from mining along the Salween or its tributaries. Political upheaval since the February 2021 military coup has blocked independent monitoring, and international researchers have had little access to active mining zones. Thai officials interviewed by the AP flagged cross-border contamination concerns, but their observations reflected downstream impacts rather than direct measurement at the pollution source.
The timing of available data compounds the uncertainty. The most recent peer-reviewed groundwater chemistry from Myanmar was published before 2021. Conditions may have shifted considerably since then, particularly as rare earth demand has surged and extraction has spread into previously untouched areas. As of early 2026, no updated peer-reviewed sampling from the Salween basin has appeared in major scientific databases.
What downstream communities can do now
For the roughly 10 million people who depend on the Salween for water, food, or both, the practical implications are immediate even if the science is incomplete. Groundwater in parts of the basin already exceeds the WHO’s arsenic safety guideline, and mining is adding to the toxic load in the broader region.
Anyone relying on well water or river-sourced drinking water in affected stretches of the basin should seek testing through local health authorities, nongovernmental organizations, or international aid groups that run water-quality programs in the region. Thailand’s public health system has the capacity to test for arsenic, and Thai officials have already raised alarms about contamination along border waterways.
On the policy side, environmental and public health groups have called for a systematic surface water monitoring program on the Salween itself. Such a program would collect water, sediment, and fish tissue samples at fixed stations over multiple seasons, measure arsenic and related metals, and publish results in formats accessible to both scientists and the public. Several organizations, including the Salween Watch Coalition and the Burma Rivers Network, have advocated for independent, cross-border monitoring since well before the current mining boom.
Why the monitoring gap matters
The Salween is roughly 2,800 kilometers long, flowing from the Tibetan Plateau through China’s Yunnan province, down through Myanmar’s ethnic states, and along the Thai border before emptying into the Andaman Sea. It is one of the few major rivers in Asia that still runs without a mainstream dam, which means its sediment and water chemistry reflect upstream conditions more directly than heavily engineered rivers like the Mekong or the Yangtze.
That free-flowing character makes the Salween both ecologically valuable and unusually vulnerable. Without dams to trap sediment, contaminants released upstream, whether from geology or from mining, travel farther and faster. Communities hundreds of kilometers downstream can be exposed to pollution they have no way of detecting without laboratory equipment.
The evidence gathered so far, peer-reviewed groundwater data showing arsenic above safe limits, investigative reporting linking regional mining to heavy metal contamination, points to a credible and growing risk. What is missing is the sustained, transparent monitoring that would turn a credible risk into a measurable one. Until that monitoring exists, millions of people along one of Southeast Asia’s great rivers are left making daily decisions about water and food with incomplete information about what those resources contain.
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*This article was researched with the help of AI, with human editors creating the final content.
