The diatom Proboscia alata was found in high concentrations at all stations in the Skagerrak and in Kat-tegat. The species diversity was generally low at all west coast stations. One or two chlorophyll maxima were found at all stations, mainly caused by P. alata and also by different species belonging to the dino-flagellate genus Ceratium. A small thecate dinoflagellate most probably belonging to the toxin producing genus Azadinium was found in relatively high numbers at the outer most station in Skagerrak. Surface aggregations could be seen from the bridge of the ship north east of Gotland and along the east coast of Öland. Small surface accumulations in forms of small streaks were also seen from sampling posi-tion close to south of Öland. Small grains of filamentous cyanobacteria were seen in the water at the en-trance of Gulf of Finland, north east of Gotland and in a large area south of Öland up to Norrköping deep. Most samples collected contained moderate to high numbers of filament of the genus Dolichospermum, Aphanizomenon flos-aquae and Nodularia spumigena* in different ratios. The absence of surface accu-mulations of these filaments were most probably due to wind stress that forced the filaments to be mixed down in the water column. The cyanobacterium Aphanizomenon flos-aquae and the genus Dolichosper-mum were found in highest concentrations in the eastern and southern parts. The only exception being the southeastern area where the toxic cyanobacterium Nodularia spumigena* appeared in higher concentra-tions. The western part of the Baltic, between Öland and Gotland, contained all three different genera but N. spumigena* was more abundant in this area. The amount of cyanobacteria in the water column in most of the Baltic indicates that as soon as the wind stress goes down surface accumulations can start to appear quickly.