Rajang River is the longest river in Sarawak. Also called Sungai Rejang or Rejang River, it flows for 563 km from the Iran Mountains in Borneo into the South China Sea.
Rajang River is known by different names through its length. The upper reaches is called Batang Balui by the Orang Ulu Bakun Hydroelectric Dam Project is located on Batang Balui Narrows.
The biggest town along the Rajang River is Sibu, 60 km from the mouth of the river. The next major town is Kanowit, at the mouth of the Kanowit River, a tributary of the Rajang. The last major town on the Rajang is Kapit. Other towns along the river includes Song and Belaga.