Surprise, The Detroit River Isn’t a River at All
The Detroit River is one of Michigan's most recognized geographic features, one of the world's busiest waterways and forms the border with Canada. But for all those things, the Detroit River is not a river.
Geographically speaking, it's a strait.
Some Strait Talk About the Detroit River
The word Detroit is French for strait, so there's your first clue about the true nature of the Detroit River. A strait is a naturally formed waterway that connects two larger bodies of water. In the case of the Detroit Strait, that would be Lake St. Clair and Lake Erie.
There are some arguments among geographers as to whether the Detroit River is technically a strait. Some would define a strait as wider than the Detroit River which reaches just over 2 miles at is widest. Compare that to the Straits of Mackinac which is five miles wide as its narrowest. And there's no one who has ever considered a Mackinac River between Lakes Huron and Michigan, which is only one lake, by the way.
On the other end of Lake Erie, a similar question can be raised about the Niagara River, which could also be considered a strait connecting to Lake Ontario.