FTP, name this river of Siberia, the 10th longest in the world, whose headwaters begin on the shores of Lake Baikal.
Its water supply increases greatly where it receives the Olyokma River.  Before that, it flows through the bottom of the Pyany Byk ravine, and receives the Vitim River, which marks the end of its upper course.  In its lower course, below the Aldan River, it enters the Yakut Lowland, bending around the Verkhoyansk Mountains before emptying into the Laptev Sea.  FTP, name this river of Siberia, the 10th longest in the world, whose headwaters begin on the shores of Lake Baikal.
Its water supply increases greatly where it receives the Olyokma River.  
Lena River