Water

Heres a little test iv done trying to create water without caustics. This image below was made by applying a texture to a directional light projecting on a plan and also placing a fog in front of it to form the foggy blue. I placed a cube into the scene and it does give the effect of being under water BUT it took literally 2 seconds to render a frame instead of the 3+minutes it took to render the caustics. I reckon we could easily get away with this as it does look very effective and the shadows work well aswell.