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Borders are shifting all the time based on how the water flows: [0] https://en.wikipedia.org/wiki/List_of_international_border_rivers https://en.wikipedia.org/

• OldHand2018 5y ago
  Yes, but in some of those cases, the borders have been set while the water hasn’t. Like this hilarity: https://www.google.com/maps/@37.1205633,-89.1155927,15z https://www.google.com/maps/@37.1205633,-89.1155927,15z
• bombcar 5y ago
  Rivers are an incredibly convenient border and also incredibly flexible over time. "Go west until you hit the river" is easy to understand and convey, and when things are measured in square miles or local it doesn't really matter, but over time that river moves and the exactitude of the boundaries matter more and more.
  • macintux 5y ago
    My uncle argued such a case before the U.S. Supreme Court: the Ohio River is gradually migrating south into Kentucky, so more of that state is now on the Indiana side of the river.