Probably not the most interesting opinion ever written by the U.S. Supreme Court, but for those historical or geographical enthusiasts, the Court's decision today in PPL Montana, LLC v. Montana makes for an interesting read. The Supreme Court basically disagreed with the Montana Supreme Court over whether or not segments of three rivers were navigable at the time Montana became a state--and therefore, whether Montana could charge rent to a company that operated dams on the river banks.  Montana said yes, but the US Supreme Court said no.  

I think the Court's decision that that the river was not navigable if you had to take your boat out of the river and walk it pass numerous falls and rapids before reentering the river has a lot of common sense behind it. 

Interesting read in that the Court describes the rivers and even cites diary entries from the Lewis and Clark expedition regarding the rivers and their navigability. 

The opinion is at http://www.supremecourt.gov/​opinions/11pdf/10-218.pdf.