I am currently making a first person deep sea underwater game, but I still cant get it to look like the player is underwater. Any tips or tricks I can use that would help get that deep sea look?
Add at script to your camera that adds fog with the blueish-green color popularly used to depict water and turn that fog on and off when it is underwater.
For the waves of light rippling across the floor that is more of a hassle. I had to create a ground mesh twice. 1 mesh includes the islands and land above water and is left intact. The second I truncated the land above my chosen sea level by intersecting the land mesh with a plane at sea level by a adding the intersect Boolean in Blender and applying. Note: the land mesh is selected and you add the Boolean to it and with the Boolean you choose then plane. Then in Unity, I use add land mesh and about + 0.025 Y axis units higher I add the sea floor mesh. Then I choose as a shader a shader with caustics and adjust it to my liking.
It gives a ‘cartoon’ type feel to the water.
If you just need at more clear type underwater effect that it feels like when you swim underwater with goggles, I’d suggest clear, almost white caustics with a little blur directly on your camera to suggest water. If the sea has plants and such you’ll need wind zones.
Wow!
Interesting. 
Wow goat - very indepth.
I was just going to suggest -
Caustic lighting and refractions
Particle floaties everywhere
Water motion variances
Depth fog
Full screen coloring effect.