The water quality in the Sai and Mekong rivers, and some parts of the Kok River, is below standard with high levels of arsenic, according to the Pollution Control Department.
The department said that it checked the quality of water regularly in the Kok River and its tributaries, Sai, Ruak and Mekong, between March and September.
It found that the samples from the Kok River, taken at the Chalerm Phra Kiat Bridge and in Tha Khao Pluek sub-district of Mae Chan district of Chiang Rai, contain high levels of arsenic, measured at 0.011-0.026mg/L.
The water in those rivers is also a murky red-brown colour, according to the department.
The department said, however, that continuous rain since July may have diluted heavy metals, such as arsenic, contained in the Sai and Ruak rivers.
Gold and other precious mineral mining activities by Chinese-funded companies in the Shan state of Myanmar have been blamed for the discharge of untreated waste water into the natural watercourses, which flow into or through some of Thailand’s northern provinces.
Thai environmental and human rights groups have been urging the Thai government to solve the problem of toxins in the rivers, but without success, because the Shan state is largely controlled by the United Wa Army, a powerful ethnic group which is independent of the Myanmar government and has close ties with China.
