ABSTRACT Assessments of stream biology are prerequisites to developing watershed management plans to improve ecological integrity. We sampled six streams in the Red River Watershed of North-Central Tennessee to evaluate the effects of non-point source pollution on diatom assemblages, primary production, and potential for excessive algal growth. We used diatom indices to assess the structure of diatom assemblages, changes of oxygen concentrations to evaluate primary production, and growth dynamics of the green alga Selenastrum capricornutum to evaluate the potential for excessive algal growth. The three most abundant diatom taxa collected were Nitzschia linearis (16%), Navicula reichardtiana (15%), and Navicula tripunctata (7%). Habitat impairment in all six streams is indicated by: (1) high Siltation Index values for diatom assemblages which indicate loss of biotic integrity as a result of excessive sediments from erosion, (2) high rates of whole-stream oxygen metabolism characteristic of eutrophic conditions, (3) low ratios of whole-stream gross primary production to respiration distinctive of heterotroph-dominated habitats often associated with poor quality water, and (4) high carrying capacities for Selenastrum capricornutum indicative of nutrient enrichment. High values of the Trophic Diatom Index and low values of the Pollution Tolerance Index of diatom assemblages at five of the six stream sites signify impairment due to eutrophication. The results reveal the impacts of excessive sediments and nutrient enrichment on the structure of diatom assemblages, oxygen dynamics, and potential for excessive algal growth in streams of the Red River Watershed.