The Nestos, Mesta is a river in Bulgaria and Greece. It rises in the Rila Mountains and flows into the Aegean Sea near the island of Thasos. It plunges down towering canyons toward the Aegean Sea through mostly metamorphic formations. At the end, the main stream spreads over the coastal plain of Chrysoupolis and expands as a deltaic system with freshwater lakes and ponds forming the Nestos delta. The length of the river is 230 km (140 mi), of which 126 km (78 mi) flow through Bulgaria and the rest in Greece. Its drainage area is 5,184 km2 (2,002 sq mi), of which 66% is in Bulgaria. It forms some gorges in Rila and Pirin. The longest gorge between Pirin to the west and the Rhodope Mountains to the east is the 25-km long Momina Klisura in Bulgaria.