ABSTRACT: Groundwater influenced by surface water is polluted by microorganisms and other substances. Microscopic particulate analysis identifies this risk, and algae prove a reliable indicator. Algal growth and reproduction cultivated in different model media supplemented with nutrients identified growth stimulation and inhibition. Herein, the monospecific Desmodesmus subspicatus algal strain was cultivated using a defined media model and subjected to the physical effects of 450 to 600 nm FAR solar radiation and 100 – 280 nm UV. Cell density was measured each 24 hours over the 3 day exposure period, and biomass concentration change was compared to biomass concentrations of control cultures grown under the same conditions. The different types of radiation combined with sufficient model nutrients result in stimulated/inhibited Desmodesmus subspicatus growth. Under certain conditions, the nutrient-enriched water can promote biomass increase which becomes a medium for secondary pathogenic microorganisms. Care is required not only to identify pathogenic and facultative pathogen propagation but also to identify autotrophic microorganisms which create biomass and can become nutrients for decomposers and consumers.