A pond appears to be shallower than it really is when viewed obliquely

Suppose two rays originate from the bottom of the pond. As these rays get refracted into the air,they bend away from the normal. When these two refracted rays are produced backwards they seem to meet at a point higher than the bottom of the pond. This point gives the apparent position of the bottom of the pond. Thus, the pond appears to be shallower. This effect is absent if the pond is viewed normally.