Phytoplankton species diversity of the Lower Vistula from Wyszogrod to Torun

In this paper, the results of research on phytoplankton species composition along the 145 km section of the Lower Vistula are presented. The research was carried out during the growing season in 1998. All sites were located in the mainstream, both in the river and in the dam reservoir, which is situated in the middle part of the studied river section. As regards the number of species, diatoms and green algae were the most numerous. Most of the species were identified at the site located above the dam reservoir. The fewest number of species were identified at the sites below the reservoir. Damming the river, and therefore changing the water flow velocity, had a clear effect on the species composition and diversity of plankton algae.