[3][4] 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] The river was once taken as the southernmost border of the influence of Sultanate of Sulu on the island of Borneo in the 19th century, and hence is featured in the 1878 grant by Sultan of Sulu to British North Borneo Company.

The boundary dispute was settled in 1899 with a compromise solution of a border between these two extremities.