Mesta (Bulgarian: Места) or Nestos (Greek: Νέστος) is a river in Bulgaria and Greece. It rises in the Rila Mountains and flows into the Aegean Sea near the island Thasos. The length of the river is 230 km. It forms some gorges in Rila and Pirin. Its longest tributery is the Dospat river. The banks of the river are covered mainly by deciduous trees that extend into halfway between Bugaria and Greece where it forms the today's boundary with Macedonia (Greece) and Thrace as well as the Kavala and the Xanthi prefectures. The river later forms into a delta to the north where swamplands, wetlands and a lagoon once existed except in the east. Rila Mountain, Bulgaria The Rila is a mountain range in western Bulgaria. ... the Aegean Sea The Aegean sea as seen from the island of Santorini The Aegean Sea (Greek: Αιγαίον Πέλαγος, Aigaion Pelagos; Turkish: Ege Denizi) is an arm of the Mediterranean Sea, located between the Greek peninsula and Anatolia (Asia Minor, now part of Turkey). ... Thasos, is the name of an island in the north of the Aegean Sea, off the coast of Thrace and the plain of the river Nestus (during the Ottoman times Kara-Su). ... The Pirin Mountains (Bulgarian: Пирин) are a mountain range in southwest Bulgaria, with Vihren (2,915 m high) the highest peak, situated at 41°4550N 23°2530E. The range extends about 40 km northwest-southeast, and about 25 km wide. ... Macedonia (Greek: Μακεδονία, IPA /maceðonia/) is the largest and second most populous region of Greece, comprising the north of that country. ... Thrace is a historical and geographic area in south-east Europe spread over southern Bulgaria, north-eastern Greece, and European Turkey. ... Kavala prefecture (Greek: Νομός Καβάλας Nomos Kavalas) is a prefecture in eastern Macedonia. ... Xanthi (Greek: Ξάνθη) is one of the fifty-one prefectures of Greece. ...