Varbitsa is a river in the Eastern Rhodope mountains. The Varbitsa river, a tributary to the Arda, the main river of the Rhodope Mountains, runs through 8 municipalities, 6 of them within the region of Kardjali and 2 in the region of Smolyan. It is the lifeline of this area, with industrial, drinking and irrigation water coming out, and refuse, raw sewage and industrial waste going in. The fact that the Varbitsa starts below an officially safe tailings reservoir above Zlatograd has also been of concern, as has been the fact that Zlatogradís own rubbish dump is next to the river, and begins to enter into its waters as it expands. The Varbitsa is Bulgariaís most temperamental river, with up to 5 000 times difference in water volume between spring highs and autumn lows, with frequent massive flooding and erosion as a result. Flooding and erosion are also stimulated by forestry and gravel industries, many of them unlicensed corrupt adding to the difficulty of control.