The river flows in the eastern area of Kalimantan with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).[3] The annual average temperature in the area is 23 °C. The warmest month is April, when the average temperature is around 24 °C, and the coldest is January, at 22 °C.[4] The average annual rainfall is 2835 mm. The wettest month is December, with an average of 332 mm rainfall, and the driest is August, with 154 mm rainfall.[5]