Long-term changes of bacteria (BAC), phytoplankton (PHY) and zooplankton (ZOO) were investigated in three Czech reservoirs with different retention times. Averages for "warm" (April to September) and "cold" (October to March) periods were evaluated for two 10-12 years’ data sets: 1959 - 1969 in the Slapy and Klicava reservoirs and 1979-1985 plus 1993-1997 in the Slapy and Rimov reservoirs. BAC numbers and exceptionally also ZOO biomass during some years showed a lower "warm" biomass than the preceding "cold" one and vice versa. Interannual changes of BAC and ZOO in the pairs of reservoirs were synchronized, BAC showed the strongest coherence, ZOO was significantly synchronized between the Slapy and Klicava reservoirs in the first data set, but not significantly between the Slapy and Rimov reservoirs in the second data set. Interannual changes of now showed lower coherence between the pairs of the reservoirs than BAG, whereas PHY interannual dynamics showed negligible coherence during 1959-1969. BAC in warm periods were positively correlated with PHY to ZOO biomass ratios in the preceding cold periods in the Slapy and Klicava Reservoirs during 1959-1969. Coherent changes of BAC land ZOO) in different reservoirs suggested an effect of meteorological variables, and/or a control (with a time delay) by biotic variables induced by interannual fluctuations of climatic factors.