Plum Island (Wisconsin)
Plum Island is an island in Lake Michigan in the southern part of the town of Washington in Door County, off the tip of the Door Peninsula in the U.S. state of Wisconsin. The uninhabited island has a land area of or . Carp Lake is located on the northwestern side. During years when Lake Michigan's water levels are high, it is a lagoon of Lake Michigan, but it gets cut off as a separate lake during low water years. The island is a bird sanctuary under control of the United States Fish and Wildlife Service and  part of the Green Bay National Wildlife Refuge. and is also open to the public for recreational purposes. The island also holds the unmanned Plum Island Range Lights. History. The border between Wisconsin and Michigan was originally defined as "the most usual ship channel" into Green Bay from Lake Michigan but commercial routes existed both to the north and south of the island which led to a border dispute. In 1936, the U.S. Supreme Court decision "Wisconsin v. Michigan" found that Plum and other nearby islands were part of Wisconsin.