The Balkan Mountains form a water divide between the rivers flowing to the Danube in the north and those flowing to the Aegean Sea in the south. However, they are crossed by Bulgaria's widest river, the Iskar, which forms the spectacular Iskar Gorge. Rivers that take their source from the Balkan Mountains and flow northwards to the Danube include the Timok, Archar, Lom, Tsibritsa, Ogosta, Skat, Vit, Osam, Yantra, and Rusenski Lom. The mountains are also the source of the Kamchiya, which flows directly into the Black Sea. Although not so abundant in mineral waters as other parts of Bulgaria, there are several spas such as Varshets, Shipkovo and Voneshta Voda.