Seasonal sampling was carried out at four sites on a pampean stream that receives industrial effluent from two textile factories. To evaluate water quality, several physical and chemical parameters were examined and the periphyton growing on cattail (Typha latifolia L.) were analyzed. Water quality and periphyton structure differed significantly between sites upstream and downstream of the discharge. Differences in temperature and also in concentrations of phosphate, dissolved oxygen, and phaeopigment were detected. At the same time, changes in the dominant algae groups were observed. Downstream of the industrial discharge, the number of Bacillariophyta decreased, while species of Cianophyta and Euglenophyta were more abundant. This abundance correlated with increased phosphate and organic matter content and decreased oxygen concentration. Although this study did not detect a reduction in the number of species, similarity between stands decreased downstream of the industrial discharge. Changes in community structure were readily detected in this situation because the communities of the polluted and unpolluted zones were qualitatively different. Periphyton growing naturally on Typha latifolia is a useful indicator of the impact of waste waters on the biota and can also be used to evaluate water body recovery.