Harsens Island is a wet marshy location at the mouth of the St. Clair River on Lake St. Clair, in the U.S. state of Michigan. Politically, the island is in Clay Township of St. Clair County.
The St. Clair River is an integral part of the Great Lakes, draining water from Lake Huron down into Lake St. Clair. Lake St. Clair then empties into the Detroit River, which flows into Lake Erie. The delta was formed about 6,000 years ago and long was a desired area of habitation by indigenous peoples.
The St. Clair River is the international boundary between the United States and Canada. The river carries more freighter traffic than the Suez and Panama Canals combined. Over 1 billion US gallons (3,800,000 m) of fresh water per day flow down the St. Clair River, and through its delta region, the St. Clair Flats.
Harsens Island is the major U.S. island in the Flats and the only one to be accessible by auto ferry. The Canadian side of the Flats has the largest islands in the delta, including Walpole Island, which are among six islands controlled by the Walpole Island First Nation, made up of Ojibwa, Potawatomi, and Odawa peoples.
The St. Clair Flats supports a range of wildlife, such as the great blue heron, snapping turtles, watersnakes, muskrats, mink, whitetail deer, pintail, canvasback and mallard ducks, Canada geese and red-winged blackbirds. The area is a popular fishing spot, as yellow perch, large and small mouth bass, rock bass, carp, sunfish, pumpkinseed fish, bluegills, and silver bass are available. The State of Michigan owns about 75% of the area of Harsen’s Island, and manages waterfowl and wildlife sanctuaries throughout.