The Barito River is the second longest river in Borneo after the Kapuas River with a total length of 1,090 km (680 mi) and a drainage basin of 81,675 square kilometers (31,535 sq mi) in South Kalimantan, Indonesia. It originates in the Muller Mountain Range, from where it flows southward into the Java Sea. Its most important affluent is the Martapura River, and it passes through the city of Banjarmasin.

Borneo is the third-largest island in the world, with an area of 748,168 km2 (288,869 sq mi). Situated at the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda Islands, located north of Java, west of Sulawesi, and east of Sumatra.