Very cool!
If I may chime in on the render settings in relation to the water reflections...
I think in this particular case it would be interesting to try the following settings:
Detail 0.8, AA12 @ 1/16th and pixel noise threshold @ 0.025 (default of AA12 anyway).
For the water reflections you disable the reflections in the water shader, by setting master reflectivity to 0.
Then connect a "reflective shader" in between the water shader and the lake object and let that shader do the reflections for you.
Enable raytraced reflectionsin the reflective shader and set the reflection roughness to a very small value, like 0.001.
The default 4 rays for reflections is usually sufficient, so no need to increase that.
The reflections take quite a while longer now, but detail 0.8 and AA12 with adaptive sampling may compensate a bit for it.
I'm curious to see a vertical crop of the centre 1/3rd of the image or so
Cheers,
Martin