Chlorella is common throughout North America
and is found in the phytoplankton of freshwater
and marine environments, often in lakes, ponds,
or small pools, and in soils. Some species (now classified by some researchers as Zoochlorella)
are endosymbionts within freshwater invertebrates such as protozoa, sponges, coelenterates, flatworms, and mollusks, forming relationships that provide the host with the benefits of Chlorella's metabolic processes such as photosynthesis and nitrogen fixation.