Not having tried this exact thing, this is generally what I'd try:
At first glance, the sunbeams look like the fibers filter, faded out and set on one of the "light" opacity settings, ex. hard light, soft light, pin light, etc. Experiment with that and see what you get.
As for the water, start with three water layers. One is the background, probably with a gradient, starting light at the horizon and deepening as it goes down. Next, have a layer for flotsam and particulates. Put your light and intermediate objects (like the water balloons) on top of this one.A filter should be useful for this. Lastly, put a layer of a solid color in front to indicate a tint from the color of the water.
EDIT: flotsam layer: monochromatic, gaussian noise on middle gray bg, then gaussian blur 1.2 px. Blend mode: multiply 60%
I'm not sure about the various blending modes, so those will obviously need some tinkering. I'm also not sure about generating the surface from this angle using filters, but there are tutorials on that from directly below
here.
Hope that helps! I'll weigh in again if I figure out a good way to get the surface from an angle, but try making a really big version of the tutorial, then using the perspective filter.
EDIT: Here's a really cheap demo of the water effect to illustrate the idea. Took about 20 mins. because I figured it out as I went. Starting from the tutorial, stock settings.
Reproducing Underwater Sunbeams
Linear Mode
