Anyway, if you run Spigot, Paper or if there is any other that can use Worldedit, you can restore chunks in your world to the aquatic level, if you have that version...

Want to restore? Simply type: 

//chunk

//regen

If you run into troubles, they can vary in:

Roads rails builds etc.. gone!

Crashing your server

Kicking you from game

Just make sure you have a backup from where you can restore sections in the world, then you are ok! If this happens and you have not noted where you were, you might find yourself in a bit of trouble: make sure to have a backup to restore that part and then try a smaller selection. No worries here, go back in, do not move at all and just type /back (if you have that command configured)

 This is just one example of the difference, left is newly regenerated and right was the old part of that world. Somehow there was ocean instead of land....

2019 09 29 20.22