Asahan River (Indonesian: Sungai Asahan) is a river in Sumatra, Indonesia, and is about 150 km long. It flows from Lake Toba, flowing in a north-easterly direction, in the upper course through the deep valley of the Barisan Mountains. The river empties into the Strait of Malacca; the city of Tanjung Balai is located at its mouth.
Coordinates: 3°02′00″N 99°52′00″E / 3.03333°N 99.866667°E