The diatom Proboscia alata was found in high concentrations in the hose samples (0-10m) taken at all stations in the Skagerrak and the Kattegat area. Distinct chlorophyll fluorescence maxima were noted at 25-30 meters at most stations. Theses maxima were all dominated by different speciesfrom the dinoflagellate genus Ceratium. No heavy surface accumulations were seen along the eastern part of the Baltic. The wind and the waves kept the cyanobacteria filaments mixed in the water column. Small aggregates visible as grains in the water column were found at all stations. These grains contained all three groups of cyanobacteria in various ratios. Some indistinct streaks were noted far away from the boat seemingly close to the east coast of Gotland. In the western part of the Baltic, from the Hanö Bight and the south of Öland, numerous grains and streaks of accumulations were visible in large areas. The toxin producing genus Nodularia* was most common in the Hanö Bight and less common in the sound of Kalmar and south of Öland. In the central parts of the Baltic between Öland and Gotland large patches of surface accumulations were present. The lack of wind and waves had enabled the filaments to float up to the surface and accumulate in patches or large streaks.