Spring bloom was primarily ongoing in the Kattegat, with high abundances of the diatoms Skeletonema marinoi and Thalassiosira nordenskioeldii. The chlorophyll peaks at Fladen and Anholt (Kattegat) were also dominated by Skeletonema marinoi. All stations had similar species composition, although the dominance of certain species was more prominent in Kattegat compared to Skagerrak (only station Släggö could be sampled this month). The integrated chlorophyll concentrations (0-10m and 0-20 m) were higher than normal for this month in the Kattegat, and within the normal range at Släggö. Diversity and cell abundance of phytoplankton were low in the Baltic Sea, with mostly smaller cells such as Cryptomonadales and smaller Gymnodiniales as well as various ciliates. Some chains of Skeletonema marinoi were found at several stations. The integrated chlorophyll concentrations (0-10m and 0-20 m) were a bit above normal for the month at all stations except the stations in the southwestern part.