this will be a great help for my underwater map, ill give you credit ofcourse 4.9/5 could have been improved with a better animation, but heck, i like it!
Just create two areas so that you cannot see the land in the underwater part and you cannot see the underwater part on the land part. Try to make the areas in between a bit larger so that you can make the region leak into it a bit (It works better this way, but you don't have to).
Then create a region covering the ENTIRE underwater part. If you can, make the region go off of the barriers disconnecting the water and land areas.
Use triggers to create sky (moonbeams) and fog (blue tint) effects in the selected region.
You also might want to lock the camera onto a unit so that they cant scroll between the areas =/
how you make underwater maps? just add blue fog and make fish fly. and yes, it is possible to combine land and unterwater maps, I don't know how but it is possible.