The Great Falls Reach of the Upper Missouri River in Montana cannot be navigated by boat. In that 17-mile stretch, as Lewis and Clark documented in 1805, the river cascades down nine waterfalls. The explorers’ journals are evidence in a Supreme Court case that turns on whether the Missouri and two other rivers were navigable in 1889 when Montana became the 41st state.

Though the history is esoteric, the legal issue is straightforward: can a state seek compensation for the use of a riverbed if it did not do so for a century?

The Constitution gives states control of navigable waters within their boundaries at the time of statehood and nonnavigable stretches to the federal government. If the court concludes that the Montana rivers were navigable in 1889, the state could potentially collect more than $50 million from a power company that owns hydroelectric dams, licensed by the federal government, on the rivers. The power company appealed the Montana Supreme Court ruling that the rivers were navigable routes of commerce, despite obstructions in parts. It contends the court should analyze the rivers section by section, with some stretches like the Great Falls Reach deemed not navigable.

Justice Antonin Scalia zeroed in on what makes the case quite odd: from 1891 until 2004, the state never asked for compensation from the companies. He said, “Now they come back, what, 100 years later, and they not only want to get the land back, they want to tax them for their use of it over all these 100 years?”