Complex sentence: It is in the Nelson River drainage basin and is the source of the Seine River, and lies between Ontario Highway 17 on the north and Ontario Highway 11 on the south about west of the city of Thunder Bay.
Split into simpler sentences: It is in the Nelson River drainage basin and is the source of the Seine River. The lake lies between Ontario Highway 17 on the north and Ontario Highway 11 on the south about west of the city of Thunder Bay.