Explanation

A pool of water appears to be less deep than it actually is because light rays from bottom of pool are bent away from the normal as they pass from water into the air. This makes the pool appear shallower than it really is. Because of the refraction of light. Refection of Light:Refraction is the bending of light as it passes from one transparent substance into another.Light refracts whenever it travels at an angle into substance with a different refractive index. Refraction is the bending of a wave when it enters a medium where its speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media.