I managed to make realistic underwater low visibility, but only if I make sure that the camera sees only seabed. If I look up, it still looks like a shallow fog on land where the blue of the sky shows overhead. What is needed is:- - A water surface that can have waves, read from a mesh or according to any suitable type of noise, and behaving like the real thing as regards light shining through it when the scene is below it. - A type of transparent layer over the scene that can randomly refract sunlight coming through it, to produce diffuse light.