no, unfortunately not. a cracked hole has appeared, which in some places reaches down to the bottom of the lake. Obviously, this mainly affects the places where I had built the columns. I copied the savegame and experimented a bit.The most successful attempt so far was to import the sector involved by an unchanged one from another game (e.g. r.0.0.7rg).
This at least allowed me to repair the lake. But I had to redo a few things. Thanks to CreativeMode, however, not quite so complicated. Since I primarily play on the Navesgane map, this is relatively easy to replace.