The Strymónas rises in the Vitosha Mountains of Bulgaria and flows about 400 kilometers south to the Aegean Sea in the Serres prefecture. The valley is a coal-producing area of Bulgaria. The Greek portion is a valley which is dominant in agriculture. The tributaries include the Rila river.
The ancient Greek city of Amphipolis was founded at the river's entrance to the Aegean, and the Battle of Kleidion was fought by the river in 1014. In 1913, the Greek army was involved in a deadly battle in the Kresna Gorge of the Strymónas during the Second Balkan War. The Bulgarians were defeated in the war, however, and the Treaty of Bucharest resulted in significant territorial losses for Bulgaria.
The ship Struma, which carried Jewish refugees out of Romania in World War II and subsequently sunk in the Black Sea, causing nearly 800 deaths, is named after the river.