Describe why a pond of water appears shallower that it really

An object seen in the water will usually appear to be at a different depth than it actually is, due to the refraction of light rays as they travel from the water into the air. This tutorial explores how fish, observed from the bank of a pond or lake, appear to be closer to the surface than they really are.

This was copied from google and it was posted on sep. 10/ 2018 so the information should be correct

3. dark matter

empty space could also be a simple vacuum