The objective of this study was to recognize contamination by mercury of selected aquatic organisms such as algae, aquatic vascular plants, zooplankton, polychaetes, molluscs, crustaceans and fish collected from Puck Bay in 1995-1998. The mercury concentration was measured using cold vapour atomic absorp-tion spectroscopy (CV-AAS). Some inter-species (in biota) and spatial differences in mercury concentration were observed, indicating that pollution comes from local land-based and non-point sources. However, noted mercury concentrations were relatively low and of the same magnitude as reported by other authors for other parts of the Baltic Sea.