The 23 kilometers long Cherni (black) Iskar is considered the main stem of the river, taking its source from the Chamovsko Lake (2,500 m) to the north-east of Damga Peak (2,669 m) and from there the river flows in north-eastern direction through the Govedartsi Valley, filled by the waters of the Chanakgyolski, Malyovishki and Urdini Lakes.