Taxonomic survey of representatives of genus Lepocinclis (Euglenophyceae) of a reservoir in the municipality of Triunfo (30°02'15S, 51°13'13 W), state of Rio Grande do Sul, southern Brazil. Samplings were made at 2 stations during 14 consecutive months, from February 1995 to March 1996. Three species, one variety atypical of its respective species, and one atypical taxonomic form were identified. Description of L. salina f. abtusa was complemented on the basis of collections made in four different locations of the Jacui river delta (29°56'S, 51°12'W and 30°03'S, 51°18'W). Lepocinclis salina var. salina was the best represented taxon geographically, occuring throughout the study period and in all net samples collected. Lepocinclis salina var. salina and L. salina f. obtusa were characteristic by their wide tolerance spectrum to the following environmental variables: pH, water temperature, organic matter concentration, total phosphorus, and the nitrogen series (nitrite, nitrate, ammonium, and total nitrogen) concentrations.