Please use HD settings :-)
Breakdown
The opacity and therefore reflection is based on viewing angle
I used a planar reflector probe to get nice and believable reflections in the water. The water fog (see below) killed the planar reflection so it needed to be excluded from the reflection render.
I added some surface dirt in places where the water wasn't moving that much, like near and between rocks and other static geometry. I used the generated signed distance fields for this. The signed distance field texture have limited resolution so I added a noise texture to make the edge more interesting. According to references there was a soft shadow in the murky water that I felt was interesting to investigate how to solve. I used an Exponential high fog for this.
Reusable stone with moss and surface line
To be able to reuse the one stone as much as possible I created a material for it that caped it with moss and tainted the surface line with some alga.
Conclusion
This project was interesting and I learned a ton about Unreal when doing it. Things that I found most interesting was the Distance Field that are used for shadows and dirt and how probes work.
I have also tried out a couple of other things like a surface tension shader, morph targets and day night cycle.
