The Křinice River, Kirnitzsch in German, has naturally changed course. It used to to flow in a slight loop, between the two countries, but now it flows straight.
Not a big deal except that about 40% of the border between Czech Republic and Germany is determined by waterways.
Initial findings show that the river may have straightened around 2013 when the area was last flooded.
I'm sure there must be some an official Czech-German border commission or some EU border something or other that will need to sort this out.
Until then it looks like Czechland has lost an area of about 18 x 28 meters (60 x 90 feet).