The watersheds of the Detroit and St. Clair Rivers comprise the area between Lake Huron and Lake Erie on the United States side, including Lake St. Clair itself. The St. Clair River watershed includes the Black River, Pine River, and Belle River. Over 1,200 mi2 of land drain into the St. Clair River, covering St. Clair County and parts of Lapeer, Macomb, and Sanilac counties in Michigan. (Based on the Friends of the St. Clair River website). The St. Clair River is the strait that connects Lake Huron to Lake St. Clair, while the Detroit River connects Lake St. Clair to western Lake Erie. The Detroit River watershed is approximately 700 mi2 and drains the major metropolitan area of Detroit, which is home to 4.3 million people.*
The Detroit region score was based on nine indicators with adequate data. The highest-scoring indicator was total suspended solids, while the lowest-scoring indicator was dissolved phosphorus. Read more about the individual indicator scores here.
* Information from the EPA Great Lakes AOC webpage.