 This study examined the effects of varying flow rates in the Quebechev Reservoir on the development of phytoplankton populations. The results suggest that an increase in flow rate during the summer-low-water period significantly reduces the amount of organic matter in the water and even prevents cyanobacterial blooms. Furthermore, the study concludes that the flow rate plays a significant role in the regulation of phytoplankton development, even when external organic loads are reduced. This article was authored by A.V. Rakuba.