Аннотация: Lake Vishtynetskoye is the unique waterbody in the Kaliningrad region. For the Kaliningrad region, it has not only unique morphometric and hydrological characteristics, but also the unique ecosystem. Currently, under the influence of various factors, including anthropogenic, the hydrological regime of the lake is undergoing significant changes, which in turn affects the state of its ecosystem. Currently, our researches observed the decrease in the volume of the incoming part of the lake's water balance, which leads to significant fluctuations in the level and slowdown in its flow, which is reflected in the acceleration of eutrophication processes, especially in the coastal part.