The most significant tributary of Crn Drim is the Radika River, 64.7 km long. The river springs at 2,200 meters above sea level from the peak Golema Vraca on Shar Planina. The river created one of the most attractive canyons for millions of years, penetrating the ravine sides of Bistra and Stogovo in the east and Korab and Deshat to the west. It is bordered to the south by the Debar valley, and to the north by the Shar Mountain. Radika is the only river with bifurcation in Macedonia, which provides water to two basins, the Adriatic and the Aegean basin. With channels, part of the waters of the river are brought to the Mavrovo Lake and fill it with water, and from here with underground tunnels to Vardar. Here HPP "Vrben" was built. In its course Radika receives many tributaries from which more than 10 km long are only: Mavrovska Reka, r. Ribnica and Mala Reka.