The main difference between ponds and lakes is that ponds
a. are inland bodies of water
b. do not develop self-contained ecosystems
c. are smaller than lakes
d. have easily observed currents

c. are smaller than lakes. Ponds and lakes are often indistinguishable, and rules in classifying may differ per region. But ponds are relatively smaller than lakes and more shallow. Lakes are deep  enough that light cannot penetrate the bottom of the water.

Then it is june the conclusion to the second sentence is just restating "if it is june then it is summer"