Aidar River [Ajdar]. (Map: Aidar River.) Left-bank tributary of the Donets River, 256 km long, and with a drainage basin of 7,370 sq km. Almost the entire stretch of the Aidar is within the borders of Luhansk oblast; only in its upper reaches the Aidar flows through Belgorod oblast in the Russian Federation. The river is used mainly for irrigation. The city of Starobilsk is located on the Aidar.

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