Abstract
Two main systems of approach used to determine if algae can reliably indicate water quality are discussed in this paper. One approach is to observe and analyze natural communities. The effect of a pollutant can be estimated by shifts in species composition and structure of the community in this type of study. The second approach studies a single or a few species in cultures in the laboratory under known and carefully regulated conditions. These studies are valuable in determining the physiological and morphological changes in function rates and polymorphism due to concentration of a given chemical or physical factor.