Cross-border pollution from Myanmar’s gold mining and deforestation impacted Thailand’s Kok and Sai rivers, exacerbating flooding and contaminating water with toxic chemicals including cyanide, arsenic, and mercury. These activities, reportedly intensified since 2023 by four Chinese companies, led to ecological devastation, decimating fish populations and threatening the health and livelihoods of 1.2 million people. The September 2024 floods submerged villages including Peng Kham in Myanmar and Thaton in Chiang Mai with mud-laden water.

In response, over 700 Thaton residents rallied on March 14, 2025, for the International Day of Action for Rivers, demanding protection of the Kok River. Tests in Mae Ai district revealed alarming arsenic levels (0.026 mg/L, exceeding the 0.01 mg/L safe limit) and mercury (0.076 mg/L, above 0.05 mg/L), linked to cancer and neurological damage. Academics and civil groups petitioned Prime Minister Paetongtarn Shinawatra to negotiate with Myanmar’s junta, ethnic forces, and China, proposing a joint panel and water-quality monitoring centre.

Following public outcry against unregulated gold mines in Myanmar in early 2025, further testing revealed widespread pollution in the Mekong River, linked to rare earth mines in broader conflict-affected areas. Rights groups warned of the expansion of rare earth mining in Shan State, backed by Chinese companies.  

People living downstream in Thailand and Laos reported health impacts and loss of livelihoods. Experts warned of risks to the safety of drinking and irrigation water, as well as ecological dangers. 

On 8 June 2025, the Chinese Embassy in Bangkok responded to these allegations regarding Chinese-owned mines, saying that “Chinese companies operating abroad are required to abide by local laws and regulations”, and calling for resolution through “friendly dialogue”. This followed a large demonstration and a letter sent to President Xi Jinping by Thai civil society.  

In early July 2025, the Mekong River Commission (MRC) confirmed that levels of arsenic contamination in trans-boundary sections of the Mekong and Kok rivers exceed international safety standards. The MRC classified this as a “moderately serious” trans-boundary environmental issue, highlighting the need for regional cooperation due to the cross-border nature of the pollution. 

A November 2025 dataset identified over 2,400 unregulated mining sites across Myanmar, Laos, and Cambodia that are discharging toxic chemicals like arsenic and mercury into the Mekong and Kok rivers.

The ongoing pollution prompted residents and civic groups in northern Thailand to hold a pilgrimage from the end of May to early June 2026, urging the government to take action on this issue.

In response to widespread protests, the Chinese Embassy in June 2026 called for “friendly consultation” while asserting that the government "requires Chinese enterprises stepping out into the global market to give utmost importance to protecting and complying with environmental regulations.”

Meanwhile, the Thai government has sought international mediation from Japan and Australia to facilitate negotiations with Myanmar’s junta and various ethnic forces.

While civil groups advocate for the establishment of a joint water-quality monitoring centre, environmental experts warn that government plans to dredge the Kok River may inadvertently worsen the contamination by disturbing toxic sediments settled on the riverbed.