The species diversity among the dinoflagellates was high in the Skagerrak but it was the diatom species Proboscia alata that dominated the phytoplankton community. The Kattegat was dominated by chain forming diatom species. Proboscia alata were among the most abundant all over Kattegat with the exception at Anholt Ewhere Dactyliosolen fragilissimus and Guinardia flaccida were very common. There were no surface accumulations in the Baltic Sea. Filamentous cyanobacteria dominated the phytoplankton community from the entrance of Gulf of Finland at LL12 through the eastern to the south of Gotland at BCS-III. The situation looked the same in the Kalmar Sound, the Karlsö Deep up to BY32 outside Norrköping. Aggregates of Aphanizomenon flos-aquae were visible at all stations visited in The Baltic Sea and were very common in all samples analysed. Filaments of toxin producing Nodularia spumigena were common or present at all stations visited. Surface accumulations may develop very fast if the weather conditions are favourable.