The depth of the water affects the visibility of this phenomenon in a few ways. For one, when light hits the surface of water, it is refracted (bent). This means that when you are looking at something under water, the light is actually being bent around it. The shallower the water, the less bending of light there is. So, in shallow water objects will appear closer to their actual position than they would in deep water. Additionally, deeper waters tend to be darker because there is less light penetration. Less light means less visibility.