Complex sentence: There are numerous islands in the Detroit River; much of the lower portion of the river is incorporated into the Detroit River International Wildlife Refuge, while a portion of the City of Detroit riverfront has been designated as the William G. Milliken State Park and Harbor.
Split into simpler sentences: There are numerous islands in the Detroit River, and much of the lower portion of the river is incorporated into the Detroit River International Wildlife Refuge. The portion of the river in the city of Detroit has been organized into the Detroit International Riverfront and the William G. Milliken State Park and Harbor.