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.
Director-general of the Department of Health, Dr Amporn Benjaponpitak, confirmed the presence of both arsenic and lead in the river and warned that heavy metals pose serious health risks to the local population. These include skin rashes, diarrhoea, nausea, vomiting, and long-term dangers like skin cancer and neurological disorders.
Sources of arsenic
At the root of the crisis lies upstream mining activity in Myanmar’s Shan State, near the Kok River’s source.
Though unconfirmed as the cause, environmental groups and academic researchers point to 23 suspected gold mining sites operating without rigorous environmental impact assessments (EIAs).
With each rain, sediment-laden runoff trickles down the hills, carrying heavy metals like arsenic and lead into the river system that crosses into Thailand.
Sen Cheewapap Cheewatham, chairman of the Senate Natural Resources and Environment Committee, says: “Satellite imagery shows the presence of mining operations in the upper reaches of the river in the Shan State of Myanmar.
“These industries pose a risk of chemical contamination, evidenced by the detection of arsenic and lead in the water flowing to Thailand.”
He said the government must clearly identify whether the chemicals originate from neighbouring mining operations and find a way to solve the problem quickly.
“We cannot allow a repeat of Klity Creek,” he warned, referring to the infamous 30-year-long lead contamination tragedy in Klity Creek of Kanchanaburi that left generations of Karen villagers poisoned.
Suebsakul Kitnukorn, a lecturer at the Faculty of Social Innovation, Mae Fah Luang University, also found arsenic contamination in the Sai, Ruak and Mekong rivers in Chiang Rai’s Mae Sai and Chiang Saen districts from nine water samples collected on April 30.
The results showed arsenic levels exceeding the standard of 0.01 mg/L in several locations, with the highest recorded at 0.19 mg/L.
He raised concerns about the potential risks if floodwaters caused contamination to affect local communities: “It’s concerning. If the public comes into contact with the water, they may be at risk. We need to continue monitoring this closely.”
Arsenic in water is particularly insidious — colourless, tasteless, and odourless, it seeps silently into the body. Prolonged exposure can lead to skin lesions, organ damage, cancer, and developmental issues in children, warns the Environmental and Pollution Control Office in Chiang Mai.
In addition to finding arsenic and lead in the river, the office also found alarming levels of arsenic and other heavy metals in sediment samples collected from six spots along the Kok River in Mae Ai district, Chiang Mai, and Muang district, Chiang Rai, between March 31 and April 1.
The concentrations of other heavy metals, including lead, nickel and chromium, were also found to be in excess of national limits.
Daily life upended
The ripple effects of the contamination stretch far beyond health. At the Karen Ruammit Elephant Camp, tourism — already battered by severe floods in September last year– is badly affected.
“We lost 80% of our visitors after the arsenic news,” said an elephant handler named Da. “No more bathing elephants in the river. No tourists, no income.”
Handlers who once earned 2,000 baht a day now make almost nothing. Elephants, no longer attractions, were led into nearby forests to forage. “We’re back to survival mode,” Da added.
Downstream, farmers like Supin are watching their crops wilt as they resort to storing rainwater or digging shallow wells — but even groundwater may be at risk.
“I don’t trust the well anymore,” said 40-year-old farmer Thanet Maneekorn. “Nobody tells us if it’s safe or not.”
The growing fear and frustration led to a public outcry on April 30, when residents from 13 affected communities in Chiang Rai submitted a petition to the Chiang Rai governor.
They demanded immediate testing of surface and groundwater, sediment, and farmland; transparent and timely reporting of the results; and urgent identification and resolution of contamination sources.
They also urged access to medical screenings and community participation in crisis response planning.
“We have been advised against using the river water, leading to confusion and fear about the safety of drinking water, groundwater, and riverbank crops,” said Thaweesak Maneewan, a representative.
“People are scared, and the government must speak clearly — not in vague bureaucratic language,” he said.
Boonsri Panasawangwong, a community rights advocate in Chiang Rai, said the river is central to daily life, providing water and food. Echoing residents’ concerns, he said the ban on using the river has disrupted their way of life.
A turning point
Faced with mounting public pressure and scientific evidence of widespread contamination, the government convened a high-level emergency meeting on April 30.
Chaired by Deputy Prime Minister Prasert Jantararuangtong, the session brought together the ministries of Natural Resources, Public Health, Defence, and Foreign Affairs.
Deputy Minister of the Interior, Theerarat Samrejvanich, emphasised the urgent need for inter-agency coordination. She said the meeting also decided the Ministry of Defence and the Ministry of Foreign Affairs should gather information concerning gold mines in Myanmar.
“This is to expedite negotiations with the agencies responsible for granting mining permissions in Myanmar, to temporarily halt mining operations and improve mining practices.”
For the families who have bathed in the river’s waters and tended crops along its banks for generations, one plea remains: clean water, and a path to restore the river’s lifeblood.
The Kok River still runs, but the fight to save it is only just beginning.