The aim of this work was to inventory the species of the families Desmidiaceae, Gonatozygaceae and Mesotaeniaceae from the periphytic community of a reservoir, located in south Brazil. The samples were collected during summer and winter in the distinct regions along the river-dam bed. The substrata collected, always in the littoral region, were petioles of aquatic vegetation. In the results 45 taxa were registered, belonging to the genera Actinotaenium (1 species), Cosmarium (17), Cylindrocystis (1), Euastrum (3), Gonatozygon (1), Hyalotheca (1), Micrasterias (7), Netrium (1), Pleurotaenium (1), Spondylosium (1), Staurastrum (9), and Staurodesmus (2). Higher species richness occurred in the transition region. Euastrum denticulatum Gay and Hyalotheca dissiliens (Smith) Brébisson ex Ralfs showed 100% of occurrence, while Cosmarium abbreviatum Raciborski var. minus (West & West) Krieger & Gerloff and Pleurotaenium ehrenbergii (Brébisson) De Bary occurred in 83% of the samples.
longitudinal distribution; Periphytic algae; Zygnemaphyceae
