(in Greek, Strimon), a river in Bulgaria and Greece. The Struma is 415 km long, including 290 km in Bulgaria. It originates on the southwestern slopes of the Vitosha Mountains and drains an area of 17,000 sq km. In Bulgaria the river flows mainly through mountainous regions with narrow gorges alternating with intermontane basins, while in Greece it flows mainly through a wide valley into the Gulf of Strimon in the Aegean Sea. High water is from February to June, and low water is from August to September. The mean flow rate near the Bulgarian-Greek border is 80 cu m per sec. The maximum flow rate is approximately 500 cu m per sec.
The Struma is used mainly for irrigation. The Studena Reservoir, in Bulgaria, is on the Struma. Tributaries of the river have hydroelectric stations. The cities of Kiustendil and Blagoevgrad in Bulgaria and Serrai in Greece are situated in the valley of the Struma.