Underwater light rays
Creating an underwater scene would really benefit from visual cues such as floating particles, visibility depth, caustics and light rays. Those things would really sell it. The problem is, those are all pretty expensive when it comes to render times. Especially caustics and underwater light rays.
There is a way to “fake” the look that you need. You can trade off using caustics for using volumetrics in C4D. Using volumetric lights, you can create the crepuscular rays (God rays) that can bring an underwater scene to life.
3D artist Daniel Danielsson shows a simple way for emulating underwater rays that should work out a lot faster than using caustics.