#FOG
Gradient fog, which I am using in an underwater extravaganza myself
<g>, is an actual "block" of fog, where the coordinates are world
defined. You specify where it starts and ends, and the gradient is
applied. This way stuff can emerge from a blanket of fog. When the
camera moves up or down, or rotates up or down, it will see thicker
or thinner fog, depending on how you set it up.