The Struma or Strymonas is a river in Bulgaria and Greece. Its ancient name was Strymon. Its drainage area is 17,330 km2 (6,690 sq mi), of which 8,670 km2 (3,350 sq mi) in Bulgaria, 6,295 km2 (2,431 sq mi) in Greece and the remaining 2,365 km2 (913 sq mi) in North Macedonia and Serbia. It takes its source from the Vitosha Mountain in Bulgaria, runs first westward, then southward, forming a number of gorges, enters Greece near the village of Promachonas in eastern Macedonia. In Greece it is the main waterway feeding and exiting from Lake Kerkini, a significant centre for migratory wildfowl. Also in Greece, the river entirely flows in the Serres regional unit into the Strymonian Gulf in Aegean Sea, near Amphipolis. The river's length is 415 kilometres (of which 290 kilometres in Bulgaria, making it the country's fifth-longest and one of the longest rivers that run solely in the interior of the Balkans.