When light travels from air into water, it slows down and changes direction. This phenomenon is known as refraction.
Refraction occurs because light moves at different speeds in different mediums. In air, light travels faster than in water, which is denser. As the light wave passes from air (a less dense medium) into water (a denser medium), it bends towards the normal line, which is an imaginary line perpendicular to the surface at the point of entry.
The degree of bending depends on the angle at which the light hits the water surface and the refractive index of both air and water. The refractive index of air is approximately 1.00, while that of water is about 1.33. Because of this change in speed and direction, objects submerged in water may appear closer to the surface than they actually are.