This post effect is a little less plug & play, but stunning and will help speed up your workflow for this kind of environment!
Mainly for static or slow moving shots, this node group features: - Scalable animated caustics texture - Caustics scaled according to depth - Caustics influence - Water color picker - Water color intensity slider - Mixes final image!
A clever trick here is you use the Normal Dot to tell the node group where the caustics are to shine - From this the shadows are subtracted, and you are left with a very good light direction estimate.
Be sure to adjust your mist pass to have some color in the foreground! ;)
Open the Blend to find out how simple this setup really is!
Use entirely at your own risk.