On 2/22/2012, the Supreme Court reversed a Montana decision that found that the state held title to riverbeds under various dams and reservoirs long being used for hydroelectric power, and that PPL Montana must pay $41 million in back rent and millions more in future rent. The Court ruled on the definition of navigability for purposes of determining ownership of the riverbed. Had the state owned the land, the case could have affected electric power rates for customers in many areas.
The Court ruled unanimously that states could only assert ownership in land under rivers that were navigable at the time the state gained statehood. Current river conditions are not binding in this determination. Areas of rivers that could only be reached by portaging around obstacles are generally not navigable.