Complex sentence: The Abay--that is, the upper course of the Blue Nile--has its source near Mount Denguiza in the Choqa mountains (about), and first flows for nearly due north to the south shore of Lake Tana.
Split into simpler sentences: The Abay--that is, the upper course of the Blue Nile--has its source near Mount Denguiza in the Choqa mountains around. It first flows for nearly due north to the south shore of Lake Tana.