Wisconsin v. Michigan

Background

This dispute is between the states of Michigan and Wisconsin over the Green Bay section of their shared boundary, including several islands and nearby waters used for fishing. The original descriptions in the 1836 Acts pointed to the “most usual ship channel,” but the record shows no single clear channel. The parties previously litigated related boundary questions; a prior decree contained errors in courses and distances. A special master, Frederick F. Faville, took evidence, maps, and testimony to resolve the present question.

Reasoning

The main question was where the boundary through Green Bay should run and which state controls the islands and waters at issue. The Court found the historic evidence about a single “most usual” channel inconclusive, so it looked to principles that protect equal access to navigable waters. Because no identifiable channel existed, the Court directed a division of the bay area as nearly equal as convenient and followed long possession and acquiescence where applicable. The master’s factual findings included that “Grassy Island” and “Sugar Island” are part of Michigan’s mainland and therefore belong to Michigan. The Court corrected technical errors in the earlier decree and authorized the master to prepare an accurate, technical decree reflecting the decision.

Real world impact

The ruling fixes which state controls specific islands and portions of Green Bay and clarifies local fishing and jurisdictional rights. The special master must now produce precise courses and distances for a formal decree, which will guide enforcement by the two states and local authorities.