The Biryusa ( Russian : Бирюса , in its lower reaches also called the Ona ) is a river in Irkutsk Oblast and Krasnoyarsk Krai , Russia . The Biryusa is 1,012 kilometres (629 mi) long, with a drainage basin of 55,800 square kilometres (21,500 sq mi).
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1-740: The river has its sources in the far southwestern areas of Irkutsk Oblast, at an elevation of 2,500 metres (8,200 ft), on the northern slopes of the Sayan Mountains . From the source area the river flows north over the Central Siberian Plateau . It is crossed by the Trans-Siberian railway at Biryusinsk , which is a few kilometers west of Tayshet where the Baikal Amur Mainline starts. The Biryusa then turns northwest, and finally flows together with
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