The Subansiri River is a trans-Himalayan river and a tributary of the Brahmaputra River that flows through Tibet's Lhünzê County, Shannan Prefecture and the Indian states of Arunachal Pradesh and Assam. The Subansiri is 442 kilometres (275 mi) long, with a drainage basin 32,640 square kilometres (12,600 sq mi). It is the largest tributary of the Brahmaputra contributing 7.92% of the Brahmaputra's total flow.