The river flows in the southern area of Kalimantan with a predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification).[3] The annual average temperature in the area is 24 °C. The warmest month is October, when the average temperature is around 24 °C, and the coldest is July, at 22 °C.[4] The average annual rainfall is 2778 mm. The wettest month is November, with an average of 570 mm of rainfall, and the driest is September, with 66 mm of rainfall.[5]