Iskar proper is formed by the confluence of Beli and Cherni Iskar and remains a typical mountain turbulent river with very large inclination and dragging force before entering the Samokov valley at an altitude of 950 m. It flows through the town of Samokov and is joined by its first significant left tributary, the Palakaria a few kilometres to the north. As it emerges out of the valley the river fills the Iskar Reservoir, the largest artificial lake in Bulgaria. Downstream of the dam the Iskar flows in north-western direction and forms the 22 km long Pancharevo Gorge that divides the Vitosha and Plana Mountains in the west and the Sredna Gora mountain range in the east. There it fills the Pasarel Reservoir and Lake Pancharevo.