Ponds tend to be shallower than lakes. Ponds are bodies of water that are shallow enough to allow the sunlight to reach the surface which in turn enables vegetation to grow. Limnologists (experts who study inland bodies of water) would call this area a ‘photic zone’ and a lake an ‘aphotic zone’.
Lakes are an ‘aphotic zone’ as the sun rays can’t reach the bottom of the lake because the body of water is too deep. This also means that plants don’t grow across the surface of the lake because the sun can’t reach them.
People often distinguish the two bodies of water using size as a distinguishing variable but this is inaccurate. We call lakes ‘lakes’ because they are deeper than ‘ponds’ and the sunlight can’t reach the bottom of a lake but it can reach the bottom of a pond.