Book 30, Question 1
When does a pond count as a lake?
There is no official line, but a pond is usually small and shallow enough that sunlight reaches the bottom, so plants can grow across the whole thing.
A lake is bigger and deeper, with open water, waves, and a dark deep zone where little light reaches. Scientists also notice that lakes often have layers of water at different temperatures. A pond can warm up and freeze to the bottom much faster.