In the Baltic Sea the process of eutrophication - increasing productivity - has became accelerated in the recent century and presently it stands the major ecological problem of this sea. One of the characteristic symptoms of eutrophication is an increase of nutrient reserves in the euphotic layer during winter accumulation, providing favourable feeding conditions for the intensive development of spring phytoplankton population, the main source of organic material in the marine ecosystem. In this study an attempt was undertaken to correlate the variability of biological parameters (phyto-plankton biomass and chlorophyll concentration) determined between 1989-1998 with chemical (nutrient concentrations in winter, oxygen saturation) and physical ones (water transparency). The parameters under scrutiny are measured regularly in water of the Bornholm Deep, SE Gotland Deep and Gdansk Deep within the framework of the Baltic Sea monitoring programme. The mean annual biomass of phytoplankton and mean annual chlorophyll content in the surface (0-10 m) layer were related to winter concentrations of phosphate, nitrate and silicate. Water saturation with oxygen during vegetation season was analysed in relation to biological parameters and the same analysis was carried out for water transparency. Statistically significant correlations between the analysed determinands were found in water of the Gdansk Deep and SE Gotland Basin but not for the Bornholm Deep.