IT HAPPENS BECAUSE OF THE REFLECTION OF LIGHT IN THE POOL.THE LIGHT ENTERS FROM AIR TO WATER i.e.,DIFFERENT MEDIUMS WHICH MAKES THE LIGHT TO BEND. WHEN LIGHT BENDS WE FEEL THE WATER IN THE POOL IS LESS DEEP.THIS WILL ALSO HAPPEN WHEN WE WILL ENTER OUR HANDS OR FEET IN WATER BECAUSE OF THE SAME REASON.
