Selenga
The Selenga River is a major transboundary waterway originating from the confluence of the Ider and Delger Muren rivers in northwestern Mongolia and flowing northeast for approximately 992 kilometres (616 miles) into Lake Baikal in southeastern Siberia, Russia, where it forms the lake's extensive delta covering nearly 700 square kilometres.[1][2] Its drainage basin spans about 447,000 square kilometres, predominantly in Mongolia (around 67 percent) and the remainder in Russia, encompassing semi-arid steppes and mountainous terrain that contribute to its role as Mongolia's principal river system.[3][4] The river delivers an average annual discharge of roughly 30 cubic kilometres of water to Lake Baikal, accounting for 50 to 60 percent of the lake's total inflow and thus exerting significant influence on the world's deepest freshwater reservoir's hydrological and ecological dynamics.[3][5] Navigable for much of its length during ice-free months from May to October, the Selenga supports regional transportation, irrigation, and hydropower potential, though its basin faces pressures from mining activities and proposed dam projects that could alter sediment transport and water quality downstream.[6] The river's delta, a Ramsar-designated wetland, hosts diverse avian and aquatic species, underscoring its biodiversity value amid ongoing transboundary management challenges between Mongolia and Russia.[6]