Georgia has about 25,000 rivers, many of which power small hydroelectric stations. Drainage is into the Black Sea to the west and through Azerbaijan to the Caspian Sea to the east. The largest river is the Mtkvari (formerly known by its Azerbaijani name, Kura, which is still used in Azerbaijan), which flows 1,364 kilometers from northeast Turkey across the plains of eastern Georgia, through the capital, Tbilisi, and into the Caspian Sea. The Rioni River, the largest river in western Georgia, rises in the Greater Caucasus and empties into the Black Sea at the port of Poti. Soviet engineers turned the river lowlands along the Black Sea coast into prime subtropical agricultural land, embanked and straightened many stretches of river, and built an extensive system of canals. Deep mountain gorges form topographical belts within the Greater Caucasus.