One of the challenges of building the Trans-(*)Siberian railway was circumventing this body of water which lies north of Ulan Bator.
The western portion of this body of water contains the Small Sea Strait, which forms a passageway to its largest island of Olchon. The Angara, a tributary of the Yenisei, is the only river that flows out of this body of water located just south of the city of Irkutsk. One of the challenges of building the Trans-(*)Siberian railway was circumventing this body of water which lies north of Ulan Bator. For 10 points, name this source of roughly 20% of the world's fresh water, the deepest lake in the world located in eastern Russia.
The western portion of this body of water contains the Small Sea Strait, which forms a passageway to its largest island of Olchon.
Lake {Baikal}