river in western Siberia that is a right-bank tributary of the Yenisey River, flowing through Irkutsk oblast (province) and Krasnoyarsk kray (region) of Russia. Its length is 1,857 miles (2,989 km), and the area of its basin is 187,900 square miles (471,300 square km). The river rises near the watershed between the Yenisey River basin and that of the Lena River and flows north and then west across the Central Siberian Plateau. In its upper course, the river has a broad valley with numerous sandbanks, but after turning west its valley narrows, and there are numerous gorges and rapids. In the river basin lies the extensive Tunguska coalfield.