Sesayap River is a river in Borneo island, flowing in North Kalimantan Province, Indonesia.

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

The warmest month is April, when the average temperature is around 23 °C, and the coldest is December, at 22 °C.

[5] The average annual rainfall is 4020 mm.

The wettest month is October, with an average of 438 mm rainfall, and the driest is June, with 263 mm rainfall.