To investigate the population dynamics of Euglenophyceae, the survey had been carried out bimonthly at nine stations from October, 1991 to August, 1993. The total 44 taxa collected from this study were classified into 39 texa(including 5 varities), 6 genera, 2 families, 1 order and a total standing crops of Euglenophyceae varied from minimum of 3,665 cells/ml to maximum of 165,920 cells/ml. The important species based on abundance investigated as followes : E. proxima, E. viridis, L. texta, T. volvocina. The standing crops of Euglenophyceae showed maximum value during winter at downstrean and the significant factors for population development of Euglenophyceae were DO, BOD, phosphate, ammonia. The population density of Euglenophyceae peaked especially low water temperature