The Phylum Chlorophyta is comprised of green algae. Green algae are a diverse group of microbes and multicellular organisms that contain the same kind of pigments found in land plants such as chlorophylls a and b, as well as some carotenoids. There are four classes of green algae, two of which are commonly found in freshwater environments. Green algae rapidly grow in response to high levels of nutrients in polluted, near-shore waters and are therefore usually associated with polluted areas.