The river flows in the northeastern area of Borneo island with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification), and into the Celebes Sea.[5]
The rivermouth is fronted by a small island called Pulau Senelak. A tidal bore occurs 3 days before and after spring tides, and its wave are high and rapid and can cause considerable damage to small craft.[6]
At the end of the 19th century, this river again became a point of contention between the British North Borneo and Dutch Borneo, since the British regarded this river as its southernmost border with the Dutch, while the Dutch assumes a further northern boundary at Batu Tinagat, Tawau. The boundary dispute was settled in 1899 with a compromise solution of a border between these two extremities.[7]
