Toxic cyanobacterial blooms constitute a common problem at the global scale. The aim of the project, was to assess fish biomass and their spatial-temporal distribution patterns in the Sulejów Reservoir in relation to cyanobacterial blooms. Additionally the spatial and temporal dynamics of physical variables, inorganic nutrients, zooplankton and phytoplankton chlorophyll a were collected to help understanding which factors are controlling the development of the bloom and determine fish behavior.