The Ilga is a left
tributary of the Lena. It has its sources in the middle of the
Lena-Angara Plateau, about to the north of
Irkutsk. It flows in a roughly northern direction across the highland area as a mountain river among large boulders within a fairly straight channel. In its middle reaches it enters a wide
floodplain where it forms
meanders. Shortly before its confluence the Ilga bends and turns east. Finally the Ilga meets the left bank of the Lena by Ust-Ilga village from its mouth. The largest tributaries of the Ilga are the Ivda (Ilda) and Kichei from the right and the Typta and Tilik from the left. The river freezes between October and May.
Permafrost is prevalent in the river basin. ==Flora and fauna==