Toxic Mining Threatens the Mekong as Pollution Spreads Across Southeast Asia

More than 2,400 mines put river communities at risk

More than 2,400 mines across mainland Southeast Asia, many illegal or poorly regulated, sit along rivers and streams that communities depend on for food, farming and drinking water. A new regional inventory assembled by Stimson Center analysts using satellite images maps 366 alluvial mining clusters, 359 heap leach sites and 77 rare earth extraction zones that drain into the Mekong Basin.

Those three categories together account for 802 mapped clusters, sites and zones feeding the Mekong system. The wider inventory, the first of its kind across the region, also covers waterways connected to the Salween and Irrawaddy. It shows how mining in remote hills can threaten communities far downstream, including places where no mining takes place.

The Mekong, Asia's third largest river, supports the daily lives of more than 70 million people. It also anchors an export economy built on rice, shrimp and fish. For years, many regarded the river system as relatively clean. Now, intensive mining is releasing toxic chemicals into waterways serving hundreds of towns and villages.

Northern Thailand offers a close view of the disruption. Tip Kamlue, a farmer aged 59 in Tha Ton, once used the Kok River to irrigate her land. The Kok flows from Myanmar's hills into Thailand and eventually meets the Mekong. After authorities warned in April that its water might be contaminated, she shut down her irrigation pumps.

Groundwater now supplies her pumpkins, garlic, sweet corn and okra. The change has altered both her farming and her relationship with a river that helped sustain her family. Her experience connects the regional mining figures to a practical problem: finding water that people can safely use every day.

How pollution moves from mines to fields

Mining creates several routes for pollution to enter rivers. Digging disturbs soil and rock, waste releases chemicals, and storms can wash both into nearby streams. Sediment clouds the water, while chemicals travel with floodwaters into irrigation canals, fish habitat and household water supplies.

Floodplains become another store of contamination. These are areas beside rivers that flood periodically, often including land used to grow rice or gather river foods. Pollutants can settle there with the mud. When rain and flooding return, the deposits can be stirred up and carried farther downstream.

Alluvial mining takes place on or beside riverbeds, where miners strip sediment and sift it for gold or, in some areas, tin and silver. The work speeds erosion and releases fine particles into the water. Those particles reduce clarity and can smother the places where fish lay their eggs.

Heap leach operations use a different process. Miners pile crushed ore onto lined pads and wash it with chemicals that draw out valuable metals. The method can be used for gold, copper, nickel or manganese. Sodium cyanide is commonly used to extract gold.

Exposed rock can also produce acid drainage, which moves metals into water. Spills and waste ponds overflowing during storms allow contaminated mixtures to escape into creeks and rivers. The resulting pollution can include both particles carried by the current and substances dissolved in the water, a difference that matters when authorities choose treatment methods.

Rare earth extraction brings a different chemical burden

Rare earth elements are used in powerful magnets that help operate wind turbines, electric vehicles and many electronic devices. In mainland Southeast Asia, the dominant extraction method is in situ leaching, which means dissolving minerals from the ground where they lie.

Operators pump large volumes of water mixed with ammonium sulphate and other reagents into hillside soils. The mixture dissolves rare earths from layers of clay. A slurry containing the minerals is then collected in a series of ponds farther down the slope, while waste is often sent back into nearby streams.

This process consumes huge amounts of water and leaves a mixture of chemicals and heavy metals, including arsenic and cadmium, that can persist in the environment. Its effects can extend beyond the extraction area as contaminated water and sediment move through connected waterways.

Dr Tanapon Phenrat, a senior researcher with Thailand Science Research and Innovation, led testing in 2025 on the Kok River. His team detected arsenic and heavy rare earths, including dysprosium and terbium. Thai researchers described the contamination pattern as consistent with new rare earth and gold mining upstream in Myanmar.

Phenrat connected the findings to the speed of the mining expansion and warned about continued releases:

It has only been two years since the rise of rare earth and gold mining in Myanmar at the Kok River's source. We are already seeing arsenic and heavy rare earths in the river, and levels will rise sharply unless the mining is stopped.

The findings place the Kok at the meeting point of two problems: extraction that uses chemicals to release minerals from soil, and a river network that carries the resulting waste across a national border.

Conflict and weak oversight allow mining to expand

Myanmar has become a major source of heavy rare earths since the military seized power in 2021. Its mining boom is tied to the war economy. Armed groups and militias in border areas raise money by taxing extraction and trade where government oversight is limited.

Forests have been cleared for access roads, hillsides marked with pits and ponds, and streams that once ran clear now run brown. Across large stretches of the Mekong Basin, overlapping jurisdictions and conflict weaken the enforcement of national laws.

Brian Eyler, a senior fellow at the Stimson Center, described how those conditions allow intensive mining to spread:

The scale is striking to me. So much of the Mekong Basin sits outside effective national laws and sensible regulations, and that makes it ripe for unregulated activity at a very high level of intensity.

Analysts who assembled the inventory said the extent of mining along tributaries of the Mekong, Salween and Irrawaddy should alarm governments that rely on these rivers for food security and economic growth. The difficulty is that the places producing pollution are often also places where public authorities have little control.

Myanmar's minerals enter global supply chains through China

Raw materials extracted in Myanmar typically travel by truck to China for processing. China has a near monopoly over the complex steps that turn rare earth oxides into powerful magnets used in wind turbines, electric vehicles and defense systems.

Mines in Myanmar and Laos often depend on technicians from China with experience in in situ leaching. The technique was refined inside China before stricter environmental rules shifted much of the extraction across the border.

China's Foreign Ministry, responding to questions about environmental performance abroad, pointed to requirements for Chinese companies investing overseas:

The Chinese side has consistently required overseas Chinese enterprises to conduct their production and business operations in accordance with local laws and regulations, and to adopt stringent measures to protect the environment.

The supply chain connects remote mining districts to manufacturers serving global markets. Producers of magnets and electronics therefore have a role in checking where their materials come from and requiring evidence that extraction meets environmental standards. Such checks depend on information reaching buyers from places where oversight is often thin.

Thai tests show arsenic and heavy rare earths

Thailand's Department of Pollution Control reported arsenic levels near four times the World Health Organization guideline in some Kok River samples following the latest mining surge. The river runs through Chiang Rai before joining the Mekong.

Researchers also detected heavy rare earths in the water and sediment, a sign of active releases upstream. Current testing does not cover every possible pollutant. Some scientists have called for screening that includes radioactive elements associated with rare earth deposits.

Arsenic exposure over time is linked to cancers of the skin and internal organs, as well as cardiovascular disease. Mercury damages the nervous system. Cadmium harms the kidneys and can weaken bones. These substances can reach people through drinking water, fish and shellfish, or crops irrigated with polluted water.

Children, pregnant women and older adults face particular risks because exposure can have cumulative effects. Repeated contact over time makes the safety of everyday water and food supplies central to the response, alongside testing the river itself.

Villagers have reported skin rashes and blisters after contact with river water. Fish catches have fallen, and livestock have suffered similar symptoms after wading in or drinking from streams that now run turbid. For communities beside the Kok and Mekong, the warning signs extend from test results to farming, fishing and daily routines.

A damaged river changes livelihoods and floods

Tip Kamlue's move to groundwater has kept irrigation going, but her concerns reach beyond a single growing season. The Tha Ton farmer described the loss of a river that once provided food, recreation and water for her crops:

It is like half of me has died. I want the Kok River to be the way it used to be, where we could eat from it, bathe in it, play in it and use it for farming.

Flooding spreads the damage beyond the river channel. During recent rainy seasons, high flows have pushed contaminated mud across low lying fields, coating rice paddies and orchards. Cleaning up that material is costly and slow.

Tourism also faces risks in communities whose attractions depend on river life. Rafting, fishing and cultural festivals centered on clean water all become harder to sustain when residents and visitors are concerned about contamination.

The sequence of developments shows how the regional mining boom has reached local households:

• 2021: Myanmar's military seized power, after which the country became a major source of heavy rare earths.
• The three years preceding November 24, 2025: Satellite analysis identified more than two dozen rare earth mines in northern Laos.
• April 2025: Authorities warned that the Kok River might be contaminated, prompting Kamlue to stop pumping its water onto her crops.
• 2025: Testing led by Phenrat detected arsenic, dysprosium and terbium in the Kok River.

Laos creates another route into the Mekong

Satellite analysis has identified more than two dozen rare earth mines in northern Laos over the past three years. Many lie within the Mekong Basin and near protected areas, creating another potential route for mining waste to enter the river system.

Laos nominally bans rare earth extraction, yet operations have appeared in remote districts where oversight is thin and pressure for investment is strong. Some projects may have local permission without approval from the central government.

Pollution entering the Mekong from Laos can move into the mainstream and onward to Cambodia and Vietnam. Cambodia depends heavily on fish from the Tonle Sap and the Mekong. Vietnam's delta relies on the river for irrigation and drinking water.

Contaminated runoff and sediment containing metals can also affect dam reservoirs. Poorer water quality and damage to turbines add a concern about reliable energy supplies to the threat facing public health and food production.

The connections between tributaries, the main river, reservoirs and the delta mean that national responses alone have limited reach. Water carries pollution across borders, while responsibility for mines and their waste remains divided among different authorities.

Thailand sets up three task forces

Thailand has announced three task forces to address the threat. One focuses on international cooperation with neighboring countries so that upstream sources can be identified and addressed. Another monitors public health along affected rivers and prepares guidance for clinics that may see increases in illnesses related to contamination.

The third works on water security for communities along the Kok, Sai, Mekong and Salween. Its responsibilities include alternative water supplies and more frequent testing, linking the immediate need for usable water with the longer task of reducing pollution.

Local groups in Chiang Rai and Chiang Mai are organizing volunteers to collect samples and build community datasets. Many want official test results made public, with clear benchmarks tied to international standards.

Researchers with regional institutions say a shared monitoring network across the basin would help authorities detect problems sooner and assign responsibility for cleanup more credibly. Comparable readings from different locations would allow communities and governments to follow contamination as it moves through the river system.

Many mines, however, operate in Myanmar's conflict zones or remote parts of Laos where state authority is fragmented or contested. Cooperation across borders must therefore address both the movement of pollution and the limited power of authorities at its source.

What can reduce harm now

Drinking water systems drawing from affected rivers can add treatment steps designed to remove metals. Field testing kits can help utilities adjust treatment as conditions change. Clinics in districts facing high risks can screen for arsenic and other metals when patients have symptoms consistent with exposure.

Sediment traps and small barriers on tributaries have also been discussed. Civil engineers caution that designing and building them takes time. They can capture material carried as particles, but dissolved contaminants continue to travel with the water.

Specialists studying river pollution identify shutting down unregulated sites that discharge directly into streams as the most effective immediate enforcement measure. That requires coordination among border agencies and clear instructions for local authorities, who may face conflicting pressures.

Diplomatic engagement and pressure through trade are central to a lasting response because so much extraction occurs beyond effective state oversight. Buyers further along the supply chain, including makers of magnets and electronics, can strengthen checks on suppliers and require proof of acceptable environmental practices.

The Mekong River Commission can support a transparent data platform and a rapid response protocol to help countries act when readings exceed agreed limits. Science can identify pollution, water treatment can reduce exposure, and enforcement can address continuing releases. River communities need those efforts to work together before more contaminated water and sediment reach their farms, fisheries and homes.

Key Points

• Satellite mapping identified more than 2,400 mines along rivers and streams across mainland Southeast Asia, many illegal or poorly regulated.
• The Mekong Basin contains 366 mapped alluvial mining clusters, 359 heap leach sites and 77 rare earth extraction zones.
• The Mekong supports more than 70 million people and an export economy built on rice, shrimp and fish.
• Thai authorities found arsenic near four times the World Health Organization guideline in some Kok River samples; researchers also detected heavy rare earths.
• Myanmar's mining expansion supplies raw materials typically sent to China for processing, while new sites in Laos create further risks downstream.
• China's Foreign Ministry says Chinese enterprises abroad must follow local laws and protect the environment.
• Thailand has announced three task forces covering international cooperation, public health and water security.
• Pollution threatens farming, fishing, tourism, drinking water and dam operations, with risks extending toward Cambodia and Vietnam.