And formerly was confined to domestic American matters involving states which had coastal areas, but more recently, has been *reinterpreted* by the federal courts to include and states which have a federal waterway [river] as a boundary of that state, or adjoining any other "Federal Waterway". The Lake of the Ozarks, for instance....
Yep. Reminds me of the project dreamed up by some easterners in the 19th Century to run riverboats up the South Platte to Denver - until they found out that in places the South Platte is about a half mile wide and a foot deep. So, the Rocky Mountain Navy is pretty small. :)
At least since the time the Constitution was ratified (actually, I think the rule goes back to colonial times), federal admiralty jurisdiction has extended to all "navigable waters," which certainly included lakes and rivers. This is not a recent reinterpretation.