The best way I have found to do underwater is to make sure you have a good back drop like a rock or terrain. I think what you are seeing is your fog or haze at the horizon as it really has nothing for the light to reflect against. I hope this will assist in your scene. :) This is a basic underwater preset I have used. I know I don't have a gallery here however most of my work is done on commission and the finished product is not mine to display. But I do love the Vue software and use it along with others to make my illustrations.