A pond is a small body of water, smaller than a lake.
There is no precise definition of what distinguishes a pond from a lake. There are no legal distinctions, and there are bodies of water named "ponds" that are much larger than others named "lakes."
However, limnologists (scientists who study lakes) note that typically ponds do not show thermal stratification—the separation of water into warmer and cooler layers—and that typically sunlight reaches all the way to the bottom of a pond, with effects on the growth of plants within the pond.
Bodies of water where there is no strong water current have a tendency to fill in over time, due to siltation and plant growth. Over the course of centuries, lakes tend to become ponds and ponds tend to become wetlands. In the presence of eutrophication, as when agricultural runoff carries fertilizer into lakes, plant growth is accelerated and the process can speed up dramatically.