Utah Lake is a shallow eutrophic lake located in central Utah. It is characterized by high nutrient and silt loads and by large algal blooms in late summer and early fall. Phytoplankton samples and environmental data were taken from June through August 1974. Phytoplankton species were identified and then quantified in a Palmer counting cell. Environmental continuum theory was employed to describe algal succession and regression analysis was used to discover interactions between algal communities and the environment. Phytoplankton communities in June were characterized by high species diversity. As the lake environment became stressed in late summer due to higher turbidity, nutrient levels, and pH and decreases in available inorganic carbon,species diversity decreased. By August, the phytoplankton flora was composed essentially of only two species, Ceratium hirundinella and Aphanizomenon flos-aquae.