Original: Moving on through sparsely-populated taiga, the Yenisei swells with numerous tributaries and finally reaches the Kara Sea in desolate tundra where it is icebound for more than half the year.
Simplified: Moving on through sparsely-populated taiga, the Yenisei grows with many tributaries and finally reaches the Kara Sea in desolate tundra where it is covered with ice for more than half the year.