Has there been any thought about making watersheds into political units?

I noticed, years ago, an interesting difference between maps of Europe and maps of the United States.

In Europe, it is relatively common to find political boundaries that run along skylines and surround river valleys. (The Danube through Austria is the best example I can recall immediately, but there are plenty of others.)

In America, political boundaries often follow watercourses. Or, of course, arbitrary straight lines.

So I would say that the assumption that watersheds are NOT political units might be a specifically American perspective....