As part of an Euglenophyte's survey carried out during 2002-2006 at three different sites of Bom Jardim Creek, 13 Lepocinclis taxa were identified at species and infraspecific level. Bom Jardim Creek is a right side affluent of Caí River, Municipality of Triunfo, State of Rio Grande do Sul, and has its almost entire 10.5 km length within the Southern Petrochemical Pole area. Local climate is subtropical. Samplings were carried out monthly both for biological and abiotic analyses. Among the taxa identified, Lepocinclis fusiformis (Carter) Lemmermann emend. Conrad, L. ovum (Ehrenberg) Lemmermann var. dimidio-minor Deflandre and Lepocinclis salina Fritsch var. salina were the broadest geographically distributed ones in the creek during all five years, due to their standing to a wide range of environmental conditions. Seasonal species richness variation was observed in all creek sampling sites, summer being significantly different from all other climatic seasons of the year.