Lakes are home to predator fish species, such as pikes. Have you ever wondered how they get their food? 

Predator fishes eat smaller fishes. What do these small fishes eat? They eat small aquatic animals, such as water fleas. What do the water fleas eat, then? They eat algae. How do they gain their energy? They photosynthesize, which means that they produce their own energy with the help of energy from sunlight. 

We can use arrows to draw the structure of this food chain from the smallest organism to the largest: alga → small aquatic invertebrate → small fish → big fish.

The food chains of a lake can also be presented in the form of a food pyramid. The largest fishes are located on the top of the pyramid. Smaller organisms are located below them. The pyramid model displays the number of organisms living in a lake quite well, because there are always fewer predators than there are smaller organisms.