Don River, a major river of Russia. It is 1,220 miles (1,960 km) long, one of Europe's longest rivers. The Don begins in the Central Russian Uplands about 120 miles (190 km) south of Moscow. It flows generally southeastward to the Tsimlyansk Reservoir and Dam, then westward past Rostov to the Sea of Azov. Chief tributaries are the Donets, Voronezh, Khoper, and Medveditsa.
Although slow and winding, with marked seasonal variation in water level, the Don is navigable throughout most of its course except from December to May, when it freezes. The Volga-Don Canal links the Tsimlyansk Reservoir with the Volga River at Volgograd and provides a major shipping artery between the two rivers. Large oceangoing vessels dock at Rostov, the Don's principal port.