Its tributary, the Pebatua River, arises in Donggala Regency, Central Sulawesi, and forms the Lariang when it is joined by the Koro River from the left (south) at 1°39′50″S 120°2′47″E﻿ / ﻿1.66389°S 120.04639°E﻿ / -1.66389; 120.04639.[2] The river, as the Lariang,[3] goes on to form part of the border between Central Sulawesi and West Sulawesi and enters the Macassar Strait just past the town of Lariang.[4][5] The mouth is at 1°25′00″S 119°17′31″E﻿ / ﻿1.41667°S 119.29194°E﻿ / -1.41667; 119.29194.