When a scuba diver looks up into the air above the body of water he is diving in, any objects he sees will be in the wrong place. This is because your eyes automatically assume that the light reaching them as traveled along a straight path. Underwater, this is not the case.
This is all due to the fact that light travels slower in water than it does in air. Since this is true, any light that enters the water from the air is bent.
Also, divers underwater can only see a limited amount of the surface above them. The critical angle, which is the angle that divides where light is either internally reflected or passed through bent, of light passing from water into air is 49 degrees. The diver underwater will be unable to see anything that is less than 49 degrees above the horizon. This is clearly shown in the picture above.
Here are some quick facts about light underwater: