Moei River The Moei River forms the border between Thailand and Burma. The river is the scene of clashes between the Tatmadaw and Karen militias. Often Karen people cross the river either in order to enter Thailand as refugees or to go back to Burma. Moei River The Moei River (, , , ) is a tributary of the Salween River. Unlike most rivers in Thailand, the Moei River flows north in a northwest direction. It originates in Phop Phra District, Tak Province, flowing then from south to north across Mae Sot, Mae Ramat, and Tha Song Yang Districts, finally entering the
Sai River (Thailand) flowing through the Tachileik/Mae Sai urban area, where there is a sign marking the northern most point of Thailand just east of the border-crossing bridge —at the meeting point of Thailand Route 1 and National Highway 4 (Burma)— over the river. Finally it flows northeastwards before joining the right side of the Ruak River, a tributary of the Mekong, less than southeast of Tachileik Airport. Sai River (Thailand) Sai River (; ; ), formerly known as the River of Lawa (; ), is a river that forms the natural border between Thailand and Myanmar at Tachileik and Mae Sai Districts.