It originates in the Müller Mountain Range, from where it flows southward into the Java Sea.

Its most important affluent is the Negara and Martapura, and it passes through the city of Banjarmasin.

[6][7] This river is the location of the closest relative of the Malagasy language of Madagascar, the Ma'anyan language of Dayaks, from where settlers arrived in Madagascar (presumably in waves) from the 3rd to 10th century and from which the current island nation's population largely traces its origins.

The river flows in the southeast area of Borneo with a predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).

The warmest month is October, when the average temperature is around 26 °C (79 °F), and the coldest is January, at 20 °C (68 °F).