One thing I find that really helps to add atmosphere to your underwater scenes is to recreate the patterns of light you see dancing on the bottom surface. Cinema 4D's Caustics can take care of this for you, but it does bump up your render times quite a bit. Here's a photo of the patterns we are talking about.
I find that a good compromise if you're looking to speed up your renders is to use fake caustics and that's what I'd like to show you in this tutorial. Caustics is a great feature, but sometimes you've got to crank out your animation ASAP and faking it is the way to go!
How to Create Underwater Lighting in Cinema 4D
In this tutorial, you'll learn how to create the complex light patterns that form under water, using a technique that renders very quickly.
Although Cinema 4D supports caustics, which recreates the underwater lighting effect very accurately, the downside is that it can slow down your render times considerably due to the complex calculations involved.
Here you'll learn how to create fake caustics that render fast, to recreate the amazing light dance that appears on the ocean bed or swimming pool floor.
You'll also pick up a few tips on how to quickly create and texture underwater terrain.
Well I hope this is a useful tutorial for you. I hope I have given you the starting point necessary to be able to play with this plugin and get some incredible effects. Please let me know how you get on with it in the comments below and please post a link to your animation. I'd love to see what effects you create using this little gem of a plugin!