This review presents the present state of knowledge of the physical, chemical, and biological changes in waters of the Gulf of Gdańsk (Baltic Sea). The general characteristics of the Baltic Sea and the Gulf of Gdańsk with brief description of changes in the ecosystem are included. Among meteorological parameters describing climate in the coastal zone, water temperature changes together with considerations of precipitation and sea level are presented. It has been confirmed that the sea level rise over the past 40 yr was very distinct. Throughout the past 30 yr an evident increase in eutrophication has been observed. Therefore, changes in salinity, oxygen content, and nutrient fluctuations with special attention paid to variability in silicate, nitrate, and phosphate concentrations in the water layer are presented. Also, discussion on the presence of toxic pollutants, such as heavy metals, PCBs, PAHs, and some pesticides, in the water body of the Gulf of Gdańsk has been included. Because of their ability to bioaccumulate and biomagnify in living organisms, these substances are of crucial importance for future marine life in the Gulf of Gdańsk. Finally, biological conditions of the coastal waters of the Gulf of Gdańsk were discussed. Data show that the ecosystem structure of the Gulf of Gdańsk has undergone tremendous changes. The species pattern has changed significantly--many species have disappeared and others have become dominant.