The Ust-Ilimskoye Reservoir is the third reservoir (after Irkutskoye and Bratskoye) of the Angara cascade of reservoirs. It is situated 837 km from the Angara mouth and consists of two parts which are located on the rivers Angara and Ilim.

The general planner of this reservoir was the Institute "Hydroproject" (Moscow). The man-made lake was filled in October 1974. The Ust-Ilimskoye Reservoir is of the channel type and has seasonal storage regulation. Its water resources are widely used for electric power production, transportation and navigation, fisheries, timber-rafting and recreation.

The drainage basin of this man-made lake is situated on the Sredne-Sibirskoye plateau. The sedimentary cover of the plateau consists of the Paleozoic, Mesozoic and Cenozoic rocks. The volcanic rocks are widely spread on the reservoir's coasts.

The total cost of the power plant with the reservoir was 1,257 million rubles, the cost of the reservoir being 127.89 million rubles (in current prices at 1974)(Q, 1).