Step #4 in the One Day Morrowind Modernization: Settings Tweaks list
Featured in Mod Lists:
Total Overhaul (#358), Graphics Overhaul (#255), Expanded Vanilla (#227), One Day Morrowind Modernization (#86)
OpenMW has a configurable water shader, with several parameters that can be adjusted.
Please see the performance guide on configuring water for detailed information about what you should do with this.