 It flows eastwards across the Myanmar-Thailand border, crossing at the Thai border town of Tha Ton (, also spelled "Thaton" ).It flows to Mae Ai District, Chiang Mai Province.Most of its length in Thailand is in Chiang Rai Province where it passes Mueang Chiang Rai District after which it bends northeastwards and flows through Mae Chan, Wiang Chai and Chiang Saen districts.