river in eastern Siberia, Russia. It rises in the Stanovoy Range and flows northwestward in a huge curve to join the Lena River at Batamay. The Aldan River is 1,412 miles (2,273 km) long, the second largest tributary (after the Vilyuy) of the Lena, and drains more than 281,500 square miles (729,000 square km). Its annual discharge varies considerably both seasonally and annually. The river is navigable to Tommot but is frozen from mid-October to mid-May.