First report back:
so far, a very quick and simple change just restores the original water clarity while preserving the awesome shine, glossiness and color that Real Environment brings and looks like this:
(please ignore the white rectangle, that has nothing to do with the mod
)
Now, having said this I have to admit that I'm a bit clueless what would be realistic for the atlantic theatre. But the game's default water transparency fits my taste quite well.
The underwater view is uneffected by this, btw.