The Iskar is formed by three rivers, the Chèrni (black) Iskar, Bèli (white) Iskar and Lèvi (left) Iskar (known under the collective name Ìskrove), with the source being accepted to be the Prav (straight) Iskar, a tributary of the Cherni Iskar. After descending from the north slopes of Rila, it fills the Iskar Reservoir—the largest in Bulgaria and the Lake Pancharevo. The river runs through the outskirts of Sofia and passes through a rocky gorge in the Balkan Mountains. It flows into the Danube near the village of Gigen in Pleven Province. The Iskar is the only river to take its source from southern Bulgaria and cross the Balkan Mountains to flow into the Danube.