Blender Insight writes:
Have you ever tried to do an underwater scene in Blender and never reached the feeling that it's actually under water in your image? Your subs, divers and fishes all looks like they are in the air and not in the water?
For you I did this simple Blender 2.8 tutorial (the steps in the compositor works for 2.79 as well) on how you can use the compositor to change the most simple image in to an underwater "thing" :)
I also show how you can add particles in to the scene without making them merge in to each other (without transforming them to "rigid bodies").
Have a nice time :)