Abstract <p>As a result of long-term monitoring (1982–2021) of the species structure of zooplankton communities in the Cheboksary Reservoir, its interannual dynamics has been studied. The changes in the species structure of zooplankton communities, accompanied by changes in the water areas occupied by zooplanktocenoses, indicate continuing active dynamic processes in the reservoir ecosystem without signs of stabilization. Two types of interannual dynamics of the species structure are revealed in the main zooplanktocenoses of the Cheboksary Reservoir. The first is the typical dynamics characteristic of the right-bank river and transitional cenoses, in which, in the first years of the reservoir’s existence, the rates of their reorganization had a large value, and with the passage of time they decreased and the direction of accumulating changes was revealed. The second type of dynamics was observed in the lake zooplankton cenosis, where succession had a two-stage character with a change in the direction of reorganization. In the first years of the reservoir’s existence, there was a significant increase in the number of rotifers and paddlefish. From the fifth year of its existence, the character of reorganization changed significantly: strengthening of limnophilic features was observed with a significant increase in the abundance of branchiopod crustaceans <i>Chydorus sphaericus</i> and <i>Daphnia galeata</i>. In contrast to the first years after flow regulation, the change in the direction of cenosis reorganization occurred in the absence of significant changes in external conditions and without significant fluctuations in velocity, which suggests that this process is predominantly endogenous. In the water area of the Cheboksarskoye Reservoir, discrete zooplankton communities in terms of species structure were recorded throughout the entire observation period, with a significant increase in limnophilic features in most communities over time.</p>