Complex sentence: The narrowest part of the strait is upstream, from Chanak to Kilid Bahr at where the channel turns north and widens for to Nagara Point, then the passage turns north-east for the final to the Sea of Marmora.
Split into simpler sentences: The narrowest part of the strait is upstream, from Chanak to Kilid Bahr at, where the channel turns north and widens for to Nagara Point. From the point, the passage turns north-east for the final to the Sea of Marmora.