Arsenic Crisis in Salween and Mekong Rivers Tied to Myanmar Mining Threatens Thai Communities

River restrictions bring an upstream crisis into Thai homes

Arsenic detected in the Salween River in Thailand's Mae Hong Son province has prompted authorities in Sop Moei district to ban residents from using river water or eating fish caught from affected stretches. Early research by Chiang Mai University found arsenic levels reaching five times the national safety standard at locations in Mae Sariang, while other heavy metals were approaching unsafe thresholds.

As of November 8, 2025, Thai agencies were retesting water and fish to establish the extent of contamination and check whether seasonal conditions were influencing the results. Confirmatory findings were expected within a week. The immediate concern reaches into household routines: communities use the Salween for agriculture, livestock, fishing and washing, while floating communities depend directly on its water.

The wider concern lies upstream in Myanmar, where expanding mining operations are linked to pollution moving through rivers shared with Thailand. The Salween and Mekong systems support drinking water supplies, irrigation, fisheries and daily life on both sides of the border. Contamination in a tributary can therefore become a problem for communities far from a mine.

Researchers at the Stimson Center identified 513 rare earth mining sites across tributaries of the Mekong, Salween and Irrawaddy in Myanmar over the past decade, including at least 40 new sites opened in 2025. Mining activity has shifted from Kachin state toward Shan state, closer to Thailand.

The Thai response now combines emergency restrictions, laboratory testing, satellite analysis and calls for diplomacy. Associate Professor Surasak Boonrueang, an environmental law scholar at Thammasat University, is urging sustained engagement with Myanmar and authorities in territories controlled by ethnic armed groups, alongside immediate relief for affected families.

How mining expanded toward the Thai border

Rare earth minerals are used in smartphones, electric vehicles and wind turbines. Rising demand, together with stricter environmental enforcement inside China, has pushed more production across the border into Myanmar.

Myanmar's 2021 military coup weakened oversight and encouraged mining in frontier areas where the central military has limited control. Operators work across a patchwork of territories administered by the military, its allies and ethnic armed organizations. That division complicates efforts to inspect mines, regulate waste and establish responsibility when pollution crosses into another country.

Many operations use a process called in situ leaching. Miners pump acidic solutions into hillsides to dissolve rare earth minerals from the surrounding material. They then channel the liquid into circular ponds for processing. Heavy rain frequently causes these ponds to overflow, washing toxic mixtures into streams that feed the Salween and Mekong.

The Shan Human Rights Foundation has documented an eightfold increase in mining sites around Mong Bawk since 2015. Some new operations are only a few kilometers from towns and farms. The group has also documented leaching ponds and suspected contamination in streams such as the Pai, which passes directly through residential areas.

How pollution travels between hillsides and rivers

Myanmar's mining belt crosses watersheds, the areas of land that drain into particular rivers. Wastewater and liquid leaking from mining areas can travel west through streams such as the Kar River into the Salween, or east through channels such as the Lwai into the Mekong.

In northern Thailand, contamination has tracked through the Sai and Kok rivers before those waters merge with the Mekong. The Ruak River is also among the waterways at risk, along with stretches of the Mekong and Salween. The pollution can contain acids, arsenic and other metals carried in water or attached to sediment.

Arsenic occurs naturally in mineral deposits, but mining accelerates its release. Acid mine drainage occurs when acidic water draws metals out of rocks and soil. The resulting water can contain both acid and dissolved contaminants.

Some metals attach to mud that settles in quieter river reaches or on floodplains. Other forms remain dissolved in the water. Fine particles can travel long distances during monsoon surges, spreading contamination through connected waterways.

Thai communities downstream have described sticky mud and discolored water during periods of high flow. Researchers see the pattern of contamination as pointing toward a continuing upstream source rather than a single spill, while the current testing is intended to clarify its scale and seasonal variation.

Floods can spread contamination beyond the riverbank

Typhoon Yagi in 2024 sent floodwaters through rare earth mining zones in Shan state and inundated nearby towns. As the water receded, it drained back into the river network, carrying material picked up along the way.

Flooding in late 2024 also washed waste from mine slopes into streets and fields before the water returned to rivers. These episodes show how mining pollution can reach homes and farmland as well as the channels downstream.

Each surge can move pollutants that later remain in riverbed sediment or seep into shallow aquifers, the underground layers that hold water. Contamination can therefore persist after floodwaters disappear. Material deposited in one storm can become part of a longer problem for water supplies and agricultural land.

The documented developments span several years:

• Since 2015, mining sites around Mong Bawk have increased eightfold, according to the Shan Human Rights Foundation.
• In 2021, Myanmar's military coup weakened oversight as mining expanded in frontier territories.
• During Typhoon Yagi and flooding in late 2024, water carried waste through mining areas, towns, streets and fields before returning to rivers.
• In 2025, at least 40 new rare earth mining sites opened within the area examined by Stimson Center researchers.
• By November 8, 2025, restrictions were in place in affected Salween stretches, with confirmatory water and fish results expected within a week.

What arsenic means for health and food

Arsenic is a potent toxin. Long exposure is linked to skin lesions, cancers of the skin and internal organs, cardiovascular disease and neurological problems. Infants and children are especially vulnerable because metals can interfere with development. Pregnant women also face added risks from exposure through water and food.

Water containing arsenic at several times the drinking water standard creates concern about both direct consumption and exposure through food. Fish and shellfish can accumulate contaminants over time and pass them to people who rely on river catches for protein.

Fish and mollusks can concentrate arsenic and other metals, including lead, antimony and nickel. The restrictions on eating fish from affected Salween stretches place a particular burden on households that depend on fishing for both meals and income.

Irrigation creates another route of exposure. Contaminated water can leave residues in soil and produce, depending on the chemistry of the soil and the form of the metal. Livestock also depend on river water, extending the concern beyond drinking supplies and fisheries.

Families cannot always replace these resources easily. Buying food from outside the basin, finding another water source or changing livelihoods can carry costs that households already losing income struggle to meet. Local health workers report growing anxiety about food safety.

The losses reach farms, fisheries and tourism

Local groups estimate that river pollution has caused about 1.3 billion baht, roughly US$40 million, in losses to farming, fishing and tourism in northern Thailand. Stimson Center researchers have also been cited in connection with that estimate.

Farmers face uncertainty over irrigation water and the condition of their soils. Fishers face restrictions on catches and concerns about whether their food is safe. Tourism businesses are part of the same regional economy and share the losses associated with polluted rivers.

Residents in Chiang Rai and Chiang Mai have asked for frequent updates in plain language, clear guidance on which river stretches are safe for fishing and bathing, and maps showing clean water points. Community leaders want compensation mechanisms that respond to measured contamination without requiring lengthy legal battles.

Floating households face especially direct exposure because the river is part of their immediate living environment. For these communities, restrictions on water use affect washing, food preparation and the practical arrangements of daily life, alongside their agricultural and fishing activities.

Responsibility crosses several centers of power

Parts of northern Shan state are controlled by the United Wa State Army and other ethnic armed organizations. Other areas fall under Myanmar's military or allied groups. Any effort to reduce pollution at its source must work through that divided authority.

Community activists and Thai commentators have singled out ethnic armies for allowing the mining boom. Regional analysts point to the role of firms and financiers backed by China, describing the use of proxies and informal joint ventures that make ownership and responsibility difficult to trace.

Field sampling and hydrological tracing, which follows how water moves through a river system, are needed to connect particular mining clusters with contamination downstream. Transparent data and access to mining sites would help establish those connections and guide measures to reduce pollution.

Surasak argues that Thailand needs stronger, sustained diplomacy with Myanmar and with authorities governing territories held by ethnic armed groups. His proposed response combines action at the source with a formal process for assessing environmental risks across borders and warning communities before exposure increases.

Thailand combines laboratory tests with satellite analysis

The Pollution Control Department and the Department of Water Resources are conducting confirmatory sampling of water and fish at multiple locations. Their work follows the initial findings in Mae Hong Son and is intended to verify the extent of contamination.

The Geo Informatics and Space Technology Development Agency is helping agencies use satellite imagery and land use information to identify likely pollution sources on the Myanmar side. Satellite evidence can show where mining has expanded, while laboratory results describe what is present in river water and fish.

Mae Hong Son authorities have imposed temporary bans on river water use and fish consumption in affected Salween stretches. The broader response also requires support for people whose normal sources of water, food and income have been interrupted.

Surasak wants the Pollution Control Department to lead water quality monitoring and publish information in a form communities can use easily. He has proposed a single public alert system, a central database and a legal framework requiring environmental risks to be assessed and disclosed before mining concessions are approved.

The environmental law scholar describes a shared assessment process as a public health measure:

Transboundary impact assessments are essential to protect public health and shared ecosystems.

What a shared assessment process would require

A transboundary environmental impact assessment, or TEIA, examines risks that a project in one country may create in another. It requires developers to analyze those risks and share the findings with neighboring governments and the public.

Applied to mining between Myanmar and Thailand, such a process would require operators to disclose who is investing, where chemicals are stored and how waste ponds are lined. It would also establish baseline water quality, meaning conditions before a project begins, and explain how monitoring would continue during operations and after closure.

Thai agencies would then have a formal route to review plans, issue warnings and request measures to reduce harm before contamination reaches downstream communities. Surasak has called for a binding process supported by shared standards across borders.

Kyrgyzstan and Kazakhstan offer an example of how this can work. Agencies from the two countries tested a TEIA process for a copper and gold project near their border. The pilot created a shared platform for collecting baseline data, consulting communities and designing emergency communication procedures.

The Mekong River Agreement provides another regional starting point. It sets out rules for notifying other members about activities that may affect the river, including dam operations and major diversions. Applying that approach to mining would involve regular disclosure, joint monitoring stations on shared tributaries and agreed emergency alerts when storms cause surges in dust, acid or heavy metals.

Practical dialogue with Myanmar and China would be necessary to exchange information even when political relations are strained. Neighboring countries have a direct interest in projects capable of contaminating rivers they share.

Communities want clean water, screening and compensation

Grassroots networks in northern Thailand have pressed for continuous testing of water, soil and fish. They also want mobile clinics to screen for heavy metal exposure, alternative supplies for villages dependent on river intakes and financial support for fishers and farmers who have lost income.

Some groups are calling for a temporary halt to imports of rare earth concentrates from Myanmar until mines meet credible environmental standards. Their demands connect the immediate needs of downstream residents with the trade that supports extraction upstream.

Pianporn Deetes, Southeast Asia program director at International Rivers, has monitored the issue and reviewed satellite evidence of rare earth mining near the Thai border. She argues that extraction methods and waste management are fundamentally unsafe, leaving communities with the costs while exporters receive the profits.

Deetes described the mining process and its consequences in these terms:

These mining methods are the epitome of irresponsibility. They use harsh chemicals to dissolve the ore and store it in toxic blue ponds, before burning it to extract the minerals. The result is devastating, leaving behind dangerous contaminants in the soil, water, and air.

She is calling for coordinated action by Thailand and neighboring states to restrict illegal shipments and raise standards at the source. Community networks are also seeking faster public information and compensation tied to measured contamination.

A shared river system faces lasting pressure

The Salween runs more than 3,200 kilometers from the Tibetan Plateau through Yunnan and Myanmar and along the Thai border. One of Asia's last great rivers still flowing freely, it supports more than ten million people and a wide variety of fish, birds and mammals.

Its upper reaches are a World Heritage Site. Seasonal flows carry sediment and nutrients that sustain floodplain farming and fisheries, linking the river's natural cycle to food production and livelihoods.

Large hydropower proposals have long generated conflict and displacement. Since Myanmar's coup, illegal logging and mining have expanded in remote areas and conservation zones. Rare earth extraction adds acids and metals to headwater streams feeding the Salween, Mekong and Irrawaddy.

Researchers are urging countries farther downstream, including Cambodia and Vietnam, to test for acids and metals linked to mining because contaminants can travel through the connected river network. Thailand's immediate task is to protect exposed communities while its monitoring and diplomacy address pollution originating beyond its border.

Key Points

• Arsenic readings reached five times the national standard at locations in Mae Sariang, prompting restrictions on water use and fish consumption in affected Salween stretches.
• Thai agencies are retesting water and fish, with confirmatory findings expected within a week of November 8, 2025.
• Stimson Center researchers identified 513 rare earth mining sites across tributaries of three Myanmar river basins, including at least 40 new sites in 2025.
• Mining around Mong Bawk has expanded eightfold since 2015, according to the Shan Human Rights Foundation.
• Local groups estimate losses to farming, fishing and tourism at about 1.3 billion baht, roughly US$40 million.
• Proposals include shared environmental assessments, joint monitoring, public alerts, clean water supplies, health screening and compensation.
• Responsibility involves mining operators, investors and authorities across territories controlled by Myanmar's military, its allies and ethnic armed organizations.