AbstractMost of the tested water quality factors increase downstream coinciding with changes in the aquatic vegetation, from typical species of fast‐flowing oligotrophic waters to those of slower‐flowing eutrophic waters. Several statistic analyses were carried out to relate physical and chemical parameters with plant distribution. Five vegetation types are found in a longitudinal distribution along the river system. They are dominated by bryophytes in the initial parts before the reservoirs and by higher plants in the final parts after the reservo