Trouble beneath the calm surface

Kok River in the North brings arsenic threat to locals from gold mines across the border, write Post Reporters

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Under the scorching sun, the Kok River glimmers as it winds its way through the northern provinces of Chiang Mai and Chiang Rai, before flowing into the Mekong River. Once a lifeline for local farms, fisheries, and tourism, the river is now a source of fear and uncertainty.

Hidden beneath its shimmering surface is a toxic threat: arsenic, a dangerous heavy metal, has been detected in alarming concentrations, leaving the villagers who rely on it for their water, their livelihoods, and their health with a growing sense of dread.

In Ban Huai Kum, a quiet village in Chiang Rai’s Muang district, Supin Kamjai, 63, gazes wearily at her withered vegetables. "We've stopped using river water," she says. Her voice was hollow. "But what good does that do now?" Her hands, rough from decades of farming, gesture toward the wilting greens — a harvest that should have fed her family for months.

Nearby, Boonchai Phanasawangwong, a local community rights advocate, shares the concern: "Our children play in the river, and now they have red, itchy rashes. We don’t know if it’s from the arsenic, but no one has come to check on us."

The situation began to change in late 2024 when the once-clear water turned muddy. In Ban Kwae Wua Dam, children began developing rashes after playing in the river.

In Huai Chomphu, farmers noticed their crops wilting despite daily watering. By early 2025, laboratory tests confirmed their worst fears: the river was contaminated with high levels of arsenic.

The contamination was particularly severe in Mae Ai district, Chiang Mai, where arsenic levels reached 0.026 of a miligramme per litre (mg/L) — well above the safety standard of 0.01 mg/L. Lead was also found at 0.076 mg/L, exceeding the safe limit of 0.05 mg/L.