Chiang Mai and Chiang Rai residents have been warned after high lead and arsenic contaminants were found in the Kok River.
Authorities issued a public warning to avoid using the murky water, citing the potential health risks posed by the contaminants which exceeded safety standards.
Aweera Pakamat, director of the Chiang Mai Environmental and Pollution Control Office, said on Saturday the Kok River, which flows from Myanmar into Mae Ai, has clear water during the dry season. However, last month the water turned unusually cloudy, with reports emerging of people developing rashes after swimming.
The office took samples from the river at three different spots for testing on March 19 and found the turbidity levels at three testing points were nearly 10 times higher than the acceptable standard.
"Our tests also found lead and arsenic levels far above safety thresholds. Prolonged exposure to these toxins, particularly arsenic, can increase the risk of cancer," he said.
Authorities advised people not to consume or use the river water. If the water is to be diverted for people's consumption, it should be carefully tested in collaboration with the local water utility.
Concerns have also been raised about the water quality of the Kok River in neighbouring Chiang Rai.
The river's appearance has turned murky, and many locals suspect gold mining activities upstream in Myanmar could be the cause.
Local authorities began collecting samples for testing on March 24, with results expected in the coming days, said a source.
Dr Waranyu Chamnongprasatporn, the chief of the Chiang Mai Provincial Public Health Office, said lead exposure could cause various symptoms, including headaches, fatigue, and severe stomach pain. Arsenic poisoning, meanwhile, may lead to skin rashes, nausea, and diarrhoea.
He warned particularly vulnerable groups, including children and pregnant women, to avoid contact with the water.
The public, he said, should boil or filter the water before use. The provincial health office will keep monitoring the situation and provide medical assistance to those affected.
