Chiang Rai, Thailand — Hand-painted banners reading “Protect the Kok River” and “Bring Back Clean Water” waved above a crowd of farmers, fishers, scientists, and environmental activists as they walked along northern Thailand’s Kok River. A River Under ThreatThe Kok River begins in Myanmar’s Shan State before crossing into northern Thailand, where it flows through Chiang Rai province and eventually joins the Mekong River. In July 2025, they released findings showing increased concentrations of arsenic and other heavy metals in the Kok River downstream. While some residents have stopped fishing and avoid eating fish from the Kok River, many still depend on it for their daily survival. We swam in the river and used it every day,” said Kru Nu, a teacher from a village on the banks of the Kok River.