Monday November 24, 2025
Mongabay —
*Sources have requested pseudonyms be used to protect their identity out of fear of retaliation from the government or mining companies
BANGKOK, Thailand/RATANAKIRI, Cambodia — “When you touch the water of the O’Ta Bouk River, the mud will stick to your skin,” said Thao*. “It creates skin issues and we can’t catch fish this year anymore. It’s thick, like condensed milk. The oil from the machinery floats on the water surface, so it might affect our health, like our stomach or intestines.”
On the quiet banks where the Sesan River and O’Ta Bouk River (also known as the Prek Liang River) meet in the northeastern Cambodian province of Ratanakiri, Ta Bouk village is where Thao calls home. The O’Ta Bouk River flows some 90 kilometers (56 miles) through Virachey National Park, one of Cambodia’s oldest protected areas, before feeding into the Sesan River and providing water to Ta Bouk village, just 2 km (1.2 mi) from the park’s border.
The O’Ta Bouk has long sustained the Brao Indigenous communities who live, farm and fish along the river’s banks, providing them with clean, potable water for generations.
But Thao’s village is just one of the hundreds across the Mekong region that have seen their life-giving rivers poisoned by toxic runoff from an explosion of unregulated mining, much of this is driven by surging gold prices, rising demand for rare earth elements and limited government oversight or environmental standards.
Extensive satellite imagery analysis conducted by U.S. think tank the Stimson Center has uncovered 2,404 mines operational between 2014 and 2025 within river basins across the region — 114 of them identified as opening this year, and a further 182 appearing in satellite imagery in 2024.
Most of the mines identified, 1,868, are situated in Myanmar, and a significant amount, 518, are in Laos, along with one in Malaysia.
But even in Cambodia, where only 17 mines were found in close vicinity to rivers and streams, the impacts are already being felt keenly by communities that rely on rivers. In Thao’s case, the O’Ta Bouk River appears to be contaminated by a politically connected and unregulated gold mine upstream, that’s sending toxic runoff downstream into the Sesan River, a key tributary of the Mekong River and part of the 3S basin that includes the Sekong and Srepok rivers.
“In July, I experienced a skin issue with my foot after touching the water [from the O’Ta Bouk River],” Thao told Mongabay in November 2025. “After half an hour [my foot] was inflamed and itchy with small bumps on my skin. I went to buy medicine and after a week it disappeared.”
Thao, his sister and his 11-year-old son had all entered the water to bathe — and all developed red lesions on the parts of the skin that were submerged beneath the O’Ta Bouk. Thao showed reporters photos of his sister’s leg that were taken in July, shortly after they’d entered the water. Clusters of raised red welts can be seen speckled below his sister’s knee.
Ta Bouk village in Ta Veng district is home to more than 200 families, all of who rely heavily on the rivers and spend much of the year living and working on their plantations along the banks of the O’Ta Bouk.
Similar symptoms developed across members of the community who had entered the water, but few had access to health care; for some, Thao said, it took up to a month for the rashes to disappear.
Nearly 13 km (8 mi) northeast, further up the O’Ta Bouk River and nearly 6 km (3.7 mi) deep into Virachey National Park, lies the village of Mondul Yorn, where Chorn*, a former fisherman turned farmer, has had to abandon the water in the wake of the contamination. He also described developing itchy skin, red blemishes and inflammation after going into the O’Ta Bouk to fish.
“Before the [O’Ta Bouk] river changed I could catch 2-3 kilograms [4.4-6.6 pounds] of fish per day, but after the river changed, I had empty hands,” he said. “Now there’s no more fish in the river.”
Speaking with rangers from the provincial environmental department, who patrol within Virachey National Park that surrounds Mondol Yorn village, Chorn learned that gold mining operations had begun upstream. The rangers, he said, were convinced that the opening of gold mines between 2023 and 2024 was why the O’Ta Bouk River was devoid of fish and making people sick.
“I feel like [the company] wants to kill us, they don’t love us anymore. The river doesn’t pollute itself; it’s polluted by the company,” he said.
Tracking toxic rivers
As the Stimson Center data show, the poisoning of the O’Ta Bouk River is not an isolated incident. The spillover of chemicals associated with mining have long proved a problem for riverine communities in the Mekong region. Over the course of 2025, the situation on the Thai-Myanmar border has underscored the urgent need for government intervention on river pollution linked to unregulated mining operations.
But while these incidents have often been viewed as separate, the waterways that connect the Mekong region threaten to spread the problem downstream.
According to Brian Eyler, director of the Stimson Center’s energy, water and sustainability program in Southeast Asia, tributaries of the Mekong and the Irrawaddy rivers have the highest concentrations of mining operations. But, he said, the threat is spread across the Bilin, Irrawaddy, Salween and Sittaung river basins in Myanmar, the Lam, Ma and Mekong basins in Laos, and the Mekong Basin in Cambodia, potentially putting scores of rivers — and millions of people who depend on them — at risk from contamination.
“Testing on water, soil and sediment along these rivers should happen immediately with resources first allocated to the rivers with the highest number of mines and those that are home to the largest populations,” Eyler said. “Eventually, all rivers with mining activity should be tested. Testing should not be limited to the areas directly near the rivers’ channels because many of these rivers flood.”
Flooding, he warned, would see toxic water and sediment dispersed widely across floodplains, threatening agriculture and food security across the region. Testing the soil and groundwater of floodplains would allow authorities to tell people where it’s safe or not safe to plant crops.
Mines choke the region’s rivers
The mines identified by the Stimson Center’s satellite imagery analysis have largely not been confirmed with a visit to the site, or ground-truthed, but can be divided into three distinct types: alluvial mining, heap leaching mines extracting gold and other precious metals, and rare earth element mines.
“Alluvial mining for gold is the process of extracting sediment in the riverbed and along the riverside and extracting gold through various separation techniques including gravity techniques like sluicing, dredging and panning,” said Regan Kwan, lead researcher at the Stimson Center. “Mercury is often used alongside gravity techniques to improve the capture of gold through amalgamation.”
Between 2014 and 2025, the Stimson Center identified 1,342 alluvial mines, with 16 in Cambodia, 347 in Laos and 979 in Myanmar. But while these mines are thought to have a relatively short lifespan, the Stimson Center found 68 across the region that opened in 2024 and a further 17 that opened in 2025. Most of the mines identified are suspected to be gold mines. But without ground-truthing, it’s possible that some mining operations may be seeking tin, copper, nickel and other metals.
Another form of mining identified was heap leaching, which Kwan said entails gold ore being mined, crushed and heaped on top of an impermeable lining before being sprinkled with a sodium cyanide solution known as leacheate for several months. The cyanide dissolves the gold, and the gold-laden solution is extracted and separated from the liquid.
Only one heap leach mine was found in Cambodia by the Stimson Center; it identified 145 in Laos and 340 in Myanmar. Forty-two of the 486 total appeared to have opened in 2025, compared to 50 in 2024.
Both alluvial and heap leaching mining operations are mobile, Kwan said, with heap leaches lasting several months or longer and alluvial mines being exhausted even faster, but both have a tendency to be abandoned and then reestablished further along the river.
“As an example, observing a single river over two to three years demonstrates how miners move throughout the river system, leaving mined sites abandoned as vegetation slowly takes over the abandoned site,” Kwan said. “In both cases, there are no indications of any post-mining cleanup process or mitigation efforts.”
Chemicals, often stored in pools or tailing ponds, are often poorly contained across the region and are exposed to monsoon seasons, which can lead to chemical spillover flowing into rivers, streams and groundwater.
“The use of cyanide and mercury to separate and extract gold puts people and the environment at risk to prolonged and or concentrated exposure to the harmful chemicals,” Kwan said, detailing the various ways mercury poisoning affects the central nervous, immune and reproductive systems, along with causing symptoms described by residents across Ta Veng district.
But it’s not just people who stand to be affected: plants, animals and crops are all at risk from contamination from mercury, cyanide, chromium and heavy metals (often introduced as waste from the mining process), which threaten the soil upon which Southeast Asia’s agricultural economy is built.
In the case of Virachey National Park, the chemical contamination threatens at least 89 species of wildlife found in the park, including clouded leopards (Neofelis nebulosa), gaur cattle (Bos gaurus), endangered Asian elephants (Elephas maximus) and critically endangered Sunda pangolins (Manis javanica). Mining contamination throws the future of both Indigenous communities and threatened wildlife species into jeopardy, but the Cambodian government has so far not responded to the issue, which could flow further downstream if unaddressed.
“The region really lacks expertise in understanding how these chemicals and dangerous elements dilute as they move downstream,” said Eyler, of the Stimson Center. “Some are soluble and others are not. What we do know is that they can contaminate crops as they grow, fish and other biota in rivers, and are directly harmful to humans if consumed or exposed to the skin. A regional effort is required for effective testing and also effective messaging to people who may be exposed.”
Officials from Cambodia’s Ministry of Mines and Energy and the Ministry of Environment could not be reached for comment on the matter.
Testing the water
As the health concerns mount, residents of Ta Bouk village been forced to find alternative sources of water, mostly by digging wells, fearing for their safety should they continue to use the O’Ta Bouk River for drinking, bathing, cooking and agriculture. Their concerns have gone largely ignored by local authorities, who Thao said have visited following complaints but didn’t conduct any testing in the O’Ta Bouk or on its banks. The riverbanks now lay sticky with a toxic mud after water levels rose in the monsoon season.
“The district authorities came between June-July this year [to inspect the O’Ta Bouk River] but there’s been no action,” he said. “The water has been muddy since May this year. After they came, nothing happened.”
Mongabay spoke with 10 people across three separate villages in Ta Veng district, eight of whom had personally contracted skin conditions from entering the river. All were deeply concerned by the risk of falling sick through coming into contact with contaminated water and felt the local authorities were powerless to do anything.
While authorities have been absent in the unfolding crisis in Ratanakiri’s waterways, Mongabay reporters conducted their own testing of both water and fish from the O’Ta Bouk and at the confluence of the O’Ta Bouk and Sesan rivers, as well as soil from their banks. An independent laboratory confirmed that two fish caught from the O’Ta Bouk and Sesan rivers contained significantly higher levels of mercury — 40.5 milligrams per kilo in the fish caught in the O’Ta Bouk and 20.8 mg/kg in the one from the Sesan — than is considered safe. The U.S. Food and Drug Administration recommends people avoid consuming fish containing 0.46 mg/kg of mercury.
Likewise, a soil sample taken from the banks of the O’Ta Bouk was found to contain 24.1 mg/kg of mercury, significantly above the 7.1 mg/kg level that the U.S. Environmental Protection Agency sets as a benchmark for soil in residential areas. Water samples from both the O’Ta Bouk and Sesan tested positive for arsenic contamination, at 0.029 mg/liter and 0.035mg/l respectively — nearly three times higher than World Health Organization’s safe limit of 0.01 mg/l.
However, these samples only represent a snapshot of the water, soil and fish quality in both rivers, with Stimson Center experts urging more testing to be done in the O’Ta Bouk and Sesan rivers, as well as downstream in the Mekong River to establish a baseline that will determine a policy response. One independent expert who reviewed Mongabay’s lab results noted that while natural processes could raise contamination levels, the proximity of the gold mine to the river was a more likely explanation for the unusually high concentrations of arsenic in the water and mercury in the fish and soil.
The unabated flow of toxic chemicals from the gold mining operations upstream has left Thao and his community with little hope for the future, where freshwater resources may become scarce in Ta Bouk village. Thao said the community is afraid of the contamination, with residents fearful of eating their own crops and vegetables, while noting that fish stocks have plummeted rapidly, plunging the villagers into hardship.
“If we can no longer use the water, we might have to migrate to find other jobs because we rely on the O’Ta Bouk River,” he said. “If there’s no river water, we’ll move from this area.
“There also might be issues with food security because the locals here produce food from this area,” he added. “Some families with enough money can dig a well, but those who are poor will have to move from this area because the water is the main source of living. The pollution could spread to the Sesan River and onto other areas, like Veun Sai.”
Eleven alluvial gold mines and the only heap leaching gold mine identified in Cambodia by the Stimson Center’s data set fall within or in close proximity to a 4,000-hectare (9,900-acre) economic land concession that was awarded to Global Green (Cambodia) Energy Development. Documents seen by Mongabay show the company had previously been granted an 18,900-hectare (46,700-acre) mining exploration license inside Virachey National Park. However, it remains unclear whether Global Green was ever granted the right to extract gold.
Poisonous influence
What is clear is that Global Green is controlled by Try Pheap, an infamous Cambodian tycoon who’s been sanctioned by the U.S. government and has a long track record of illegal logging, along with mining in the Mekong and in other protected forests. Pheap has long enjoyed near total impunity in Cambodia due to his close ties to senior ruling party officials.
Combined, verified government documents, satellite imagery and interviews with residents and local officials across Ta Veng district suggest that gold mining began in mid-2023, resulting in the discoloration and pollution of the O’Ta Bouk and Sesan rivers.
One local official, who asked for anonymity for fear of speaking out against such a politically connected gold mine, recalled how armed private security denied police and government rangers access to inspect the mining site.
“Everyone knows the name, we cannot stop them,” the official said.
While an environmental impact assessment (EIA) was conducted, according to one document dated Feb. 19, 2024, the local official said the assessor — which Mongabay has since identified as E&A Consultants, a company frequently used to produce EIAs for Global Green — didn’t even visit the remote gold mining site in Virachey. E&A Consultants did not respond when Mongabay sent questions.
According to the local official, who was able to verify documents acquired by Mongabay, Global Green was only granted an exploratory license and is not permitted to extract, process or refine gold. Satellite imagery shows at least five of the alluvial mines are operating illegally outside Global Green’s concession area.
“What I’m concerned about is the natural resources in the water,” the local official said. “Mercury and acid — it’s very important that we think about this because mercury is a very bad chemical that impacts humans and wildlife. We should collect the samples in the water or wildlife that live in the area to have a laboratory [test them] to determine whether it contains these chemicals or not.”
No such tests have since been conducted, according to the official, who also questioned why the government had failed to respond to something that is so obvious to so many people across Ta Veng district.
The O’Ta Bouk is the longest river in Virachey National Park and provides a migratory link for fish species between the Sesan and Mekong rivers, but now poses a public health risk.
“If the fish are polluted with mercury, what problems could happen when humans eat them? [Global Green isn’t] following the EIA, isn’t following the law, [someone] should respond,” the local official said. “What loss will it take on the ground? What impact to the river resources? What about those living along the river, Indigenous people, who collect nontimber forest products from the area? That’s my concern.”