Abstract: The Sulejów reservoir situated on the Pilica River in Central Poland serves as an important source of drinking water for the Lodz Agglomeration. Precise knowledge on fish abundance, community structure as well as spatial and temporal changeability is crucial for proper fishery management (biomanipulation) in order to slow down the reservoir eutrophication and prevent toxic algal blooms. As the reservoir is very shallow (average depth is 3.3 m) it was necessary for fish distribution monitoring to apply, first time in Poland, horizontally looking split beam echosounder (Simrad EY-500 with elliptic transducer ES 120-4x10). Simultaneously, to collect fish for verification of acoustic data and determination of fish species composition, multimesh gill nets were used in representative parts of the reservoir. Prepared maps showing both spatial fish distribution and their density suggest that used methods were suitable for identification of specific areas characterized by different quality of environmental conditions.