Silau River is a river in northern Sumatra, Indonesia, about 1300 km northwest of the capital Jakarta. It is a tributary of Asahan River.
The river flows in the northern area of Sumatra with predominantly tropical rainforest climate (designated as Af in the Köppen-Geiger climate classification). The annual average temperature in the area is 24 ðC. The warmest month is June, when the average temperature is around 26 ðC, and the coldest is January, at 23 ðC. The average annual rainfall is 2950 mm. The wettest month is November, with an average of 381 mm rainfall, and the driest is June, with 117 mm rainfall.