The real world under water is fascinating, the world you will create even more so. There are example scenes for shallow water down to the deep sea with light rays from above and scenes to set up your own caustics with colour aberration from supplied high resolution images, everything explained in videos. A video tutorial and example scenes show how the water surface, below it and above it can be rendered in one go and how an HDRI backdrop can be blended in to complete the scene.
