Iskar (in antiquity in Latin: Oescus after the name of the Roman city of Ulpia Oescus at the mouth of the river) is the longest entirely Bulgarian river. The Iskar River rises in the Rila Mountains, collecting the waters of The Black, The Left and The White Iskar rivers. The confluence of the Black Iskar and White Iskar rivers at 1047 m above sea level is considered to be the beginning of the river. The length of the Iskar River after their confluence is 340 km, and together with the Beli Iskar River it is 368 km to its mouth. The Iskar River flows as a right tributary into the Danube River at 25 m above sea level. The area of ​​the Iskar watershed is 8646 km2. The average annual runoff at the entrance to the Gorge (town of Novi Iskar) is 23.30 m3/s. The Iskar River is the only river in the country that originates in Southern Bulgaria, but crosses the Stara Planina Mountains and flows into the Danube River. The largest dam in Bulgaria is built on it - Iskar Dam.
