About this image

I.e. Purewaters, Morrowind edition:
MGE XE + most recent MMC water shader
Underwater Effects is on. Caustic lighting has the default value of 50.

MGEXEgui settings:
Distant Land > Fog > Below Water Fog
Start: 0.0
End: 1.0
If that makes the water too clear for you, use lower values, for example -0.2 and 0.6.
If the values are grayed out and cannot be edited, disable "Auto set other distances".