The source of Thega river is within thousand feet of height inside Bangladesh. It is located approximately 10 km north of three-faced pillar hill which is adjacent to India’s border. Thega river has flowed from it. Then it has fallen to Karnaphuli and the place is called Thegamukh. From the source, a few kilometers completely flows inside Bangladesh, but in the later part it is completely separated from Mizoram to the Rangamati district. On the banks of this river there are some Chakma, Tanchanga, Marma and Pakkhoa settlements, a market and some BGB camps.