Abstract
The floristic composition, abundance, and biomass of phytoplankton in the Cybina River and the Maltański Reservoir were examined from April to October 2005. The analysis of the phytoplankton in the samples revealed statistically significant differences in both composition and abundance. The maximum abundance (39.2 × 103 ind. cm-3) and biomass (56.8 μg cm-3) of phytoplankton was noted in July 2005 at the outlet from the Maltański Reservoir. The lowest phytoplankton density was most often noted at the site located at the inlet of the Cybina River into the Maltański Reservoir. The quantitative and qualitative compositions of the phytoplankton varied at different sites. The highest taxonomical similarity was noted among the samples collected in the reservoir and at the outflow from it.