Complex sentence: Wappatoo Island, now Sauvie Island, lies just north of the main confluence of the Willamette and Columbia Rivers, with the north end of the island being the location of the confluence with the Multnomah Channel.
Split into simpler sentences: Wappatoo Island, now Sauvie Island, lies just north of the main confluence of the Willamette and Columbia Rivers. The north end of the island is at the confluence with the Multnomah Channel.