For the darker “deep” water effect when looking down from above you will need to add a depth fade node with a scalar parameter to drive a Lerp between deep and shallow colors to your translucent water material. I have an example of this in the ocean project linked in my signature below but it’s a really complex material, so I put together a quick example of how it’s used:
I created the adjustable variables as parameters rather than hard coded values, this way you can create a material instance to get the right settings for your project. To control how deep the water needs to be before you can no longer see the bottom adjust the FadeDistance parameter, and to adjust how smooth the transition is you can increase the FadeSoftness parameter.
That’s pretty much it for this effect when looking down from above, but won’t do anything below the surface.
This is a very basic implementation of it, but should do what you need. Here’s what it looks like with a similar technique in the ocean project:
In this image I’m actually using 2 different depth fades, one for the deep to shallow water, the other for the shallow to very shallow water. I’m in the middle of some big changes to this material so it doesn’t look as good as it should right now, but with with enough adjustment you can get it looking just right.
Hope that helps!