Over the period of the spring phytoplankton bloom (March-May 2009), an intensive sampling program was conducted at 2 sampling depths (0.5 m and 1% PAR) located at lacustrine zone of the canyon-shaped, meso-eutrophic Římov reservoir (Czech Republic). Changes in the production and community dynamics of epilimnetic bacterioplankton, studied by means of group-specific rRNA-targeted oligonucleotide probes, were related to shifts in composition and activity of phytoplankton, and to remarkable changes in total protistan bacterivory. It was documented that particular groups of bacterioplankton responded differently to: (i) major shifts in phytoplankton composition and its activity and to (ii) changes in overall protozoan grazing pressure.