At least between Finland and Sweden, in the Tornio/Torneå river, there are small adjustments to the border done on a regular basis, every 25 years. The previous

At least between Finland and Sweden, in the Tornio/Torneå river, there are small adjustments to the border done on a regular basis, every 25 years. The previous border adjustment was in 2006 and the one before that in 1981. The river changes a little bit as it erodes its banks, and the border is officially moved accordingly. This naturally results in minuscule changes in the land area of both countries, though in this case the changes cancel each other out in the long run. It's a friendly border.