The purpose of the study was to examine herbicide impacts upon lotic periphyton communities at concentrations that could be found in the environment. Changes in periphyton communities were evaluated by measuring total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll c indicating that agriculturally realistic concentrations of Aatrex, Roundup, and Glean have no significant decrease in periphyton biomass, measured as total chlorophyll per cm2. Chlorophyll ratios suggest these herbicides change the community composition. Roundup and Glean appear to favor eukaryotic periphyton, and...