Minnesota v. Wisconsin

Background

Two States, Minnesota and Wisconsin, disagreed about their border through Upper and Lower St. Louis Bays. Wisconsin argued for a sinuous line close to Minnesota’s shore that would cut across some Minnesota docks. Minnesota argued the boundary ran to the middle of the bays. The dispute turned on how to read 1846 law language referring to the "mouth of the St. Louis River" and the "main channel," and the parties relied on an 1861 Meade chart that both accept as showing 1846 conditions.

Reasoning

The Court considered where the river mouth and the main navigable channel were in 1846, noting later dredging and harbor work did not change that legal baseline. It applied the long-established rule that when a navigable river separates States the boundary follows the middle of the principal channel actually used for navigation. The Court rejected Wisconsin’s attempt to make the line follow a narrow deep course near the shore and instead found the main channel was the shorter, more commonly used route shown by the Meade chart and Minnesota’s marked trace. The Court set a detailed line on that chart and required a formal decree reflecting those points.

Real world impact

The decision fixes which State has authority over waters, docks, and harbor facilities in the bays based on the 1846 conditions shown on the Meade chart. It resolves who controls waters crossed by existing docks and affects regulation, taxation, and enforcement in those areas. The Court also divided costs equally and invited the States to consider adjusting boundaries by agreement with Congress.