The two other major dams on the Irkutsk Oblast's section of the Angara are at Bratsk and Ust-Ilimsk; both forming large reservoirs. The Lena has its source in Irkutsk Oblast as well, and flows north-east into the neighboring Sakha Republic.

Irkutsk Oblast consists mostly of the hills and broad valleys of the Central Siberian Plateau, with the Lena-Angara Plateau.