I suspect you've used the gradient blender exclusively in the color channel. A better method is to make your water color almost black and then apply the color to the transparency channel. In this example, I have two blue's mixed in the transparency channel and blended with an Elevation modifyer. This gives you the ability to specifically control change over distance. (make sure to check "local" in the channel option for elevation) Since Carrara doesn't have volumetric shaders, this is a useful way to fake it. In actual water scenes I use a large cylinder instead of a cube so there are no corners. I keep the base of the cylinder below the ocean bottom if there is one. The top of the water is mapped to the top surface. (parametric mapping). I used the same shader but added bump and refraction. Combining this technic with blue fog in your scene will work pretty well if you camera is underwater. Hope this helps. Mark