The water level has dropped 1.5 m below its permitted hydro-biological minimum. The river has its source in western Bulgaria (Vitosha Mountain, south of Sofia) and ends in the Aegean Sea (Strymonikos Gulf — Greece). Major transboundary tributaries include the following rivers: Butkovas, Exavis, Krousovitis, Xiropota-mos, and Aggitis, shared by Bulgaria and Greece, Dragovishtitsa, shared by Serbia and Bulgaria, Lebnitsa, and Strumica/Strumesh-nitsa shared by the former Yugoslav Republic of Macedonia and Bulgaria. The Kcrkini Reservoir in Greece was created with the construction of a levee in 1933 for regulating the river discharges, for irrigation purposes, and flood protection (a new levee was constructed in 1982). The Kerkini Reservoir was finally developed into an important wetland, protected under the Ramsar Convention. In Greece, irrigation dams also exist at Lefkogeia and Katafyio.