Data of field observations of 1989–1991 were used to analyze the habitat conditions and the structural–functional characteristics of phytoplankton in near-dam reaches of Volga reservoirs. Averaged data show negative trends, manifesting themselves in a decline in the characteristics of phytoplankton development and production–destruction processes in the lower pools of HPPs against the background of a decrease in water temperature, water transparency, and dissolved oxygen content. Saprobity indices show water quality in near-dam reaches to correspond to β-mesosaprobic zone and not to deteriorate in the lower pools, despite the decline in organic matter destruction. By the combination of abiotic characteristics and phytoplankton production indices, the upper and lower pools of Volga HPP reservoirs occupy close positions in the shortest network and fall in the clusters formed by stations in appropriate reservoirs.