Simple one celled organisms, called protozoa, are at the bottom of the food chain. These abundant, microscopic organisms allow almost all other life forms to survive in the lake. Food fish, such as minnows, shad, and bream eat the protozoa and in turn become food for predatory fish-bass, pike, and walleye. Bottom feeders, such as crayfish, catfish, and clams play an integral part in keeping the lake water clean and healthy.
Freshwater lakes are home to many other types of animal life. Arthropods, mussels, leeches, worms, and many insects all call the lake home. All of these life forms have developed ways of extracting oxygen from the water. Higher forms of aquatic life use gills similar to the way we use lungs, though gills are much more efficient. Some forms of life use the simple process of diffusion to obtain the oxygen they require.
Freshwater lakes also serve as nurseries for many types of insects, such as mayflies, mosquitoes, and dragonflies. Amphibians (frogs and toads) spend their adolescent life as gill breathing juveniles in freshwater lakes. Ducks, geese, and other aquatic birds depend on lakes to provide food and homes for their survival, too
African clawless otter
Cameroon clawless otter
North american otter
La plata otter
Indian smooth-coated otter
Giant brazilian otter
Dolphins, porpoises, and whales
Black finless porpoise
Setzer's pygmy mouse
Dugongs, manatees, and sea cows
Read more at the list of biomes of the world...