Most green algae occur in fresh water, although a few groups are marine. Some green algae is found in snow, soil, on tree trunks and in symbiosis with other organisms. Algae of this class are either unicellular, few- celled, or filamentous in nature. Most green algae belong to this class. All euglenoids but one, Colacium , are unicellular.
Most euglenoids are freshwater organisms.
These organisms are actually photosynthetic bacteria. The proper term for this group is Cyanobacteria. National standards are not currently established for algae populations. Algal blooms should be controlled by decreasing nutrient concentrations in the water body. Freshwater systems tend to be phosphorus limited.