Hi @motorsep,
With specifically the Single Layer Water material type, you’ll have to achieve this with a Distance To Nearest Surface.
At the most basic level, this is what that looks like.
If you plug it into the Alpha of a lerp for your opacity, this will have the effect of creating a natural, smooth fade in around any meshes that are near to the water’s surface.
Another way to achieve this is actually through the Absorption Coefficient. If you’re interested in that method, this tutorial breaks it down really well:
Best of luck! Let me know if you have any other questions.