Selenga (sĕlĕng-gäˈ) [key], river, 616 mi (992 km) long, rising in the Khangai Mts., NW Republic of Mongolia, and flowing east, then north, across the Mongolian-Russian border to Lake Baykal; the Orkhon River is its main tributary. The Selenga, navigable from May to October, is Mongolia's chief river; its role as a transportation artery decreased with the advent of the Trans-Baykal RR. Ulan-Ude, an important Russian rail junction, river port, and industrial center, is the largest city on the river.
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