Here are some examples of pond denizens:
* Animals: Frogs, turtles, fish, dragonflies, water striders, snails, newts, salamanders, beavers, muskrats, and more.
* Plants: Water lilies, cattails, reeds, algae, and other aquatic plants.
The term "denizen" implies that the creature lives in the pond as its home, rather than just visiting it occasionally.