Temperatures in May, ranging from 10.0 to 12.5 °C, corresponded to the long-term mean, while temperatures in June were above average, at 14.5 to 16.5 °C. In May, a marked precipitation surplus was recorded. Sea surface temperatures were largely normal in the period considered. Oxygen concentrations in the surface layer were around 100 %, in the bottom layer they were slightly lower.
In early May, a major bloom of the large diatom Coscinodiscus concinnus was observed off Norderney which lasted only a few days, however. Also at the beginning of May, an explosive increase in the foam-producing alga Phaeocystis globosa was observed in the Wadden Sea off North Sylt. A large diversity of summer phytoplankton species was observed in June. Generally, there was an increase in species diversity in all groups. Toward the end of the month, another bloom of the foam-producing Phaeocystis globosa was observed. The abundance of light-emitting Noctiluca scintillans increased. "Black spots" were hardly observed in the Wadden Sea; the areas found were very small.
At monthly temperatures between 9.0 and 11.0 °C in May, deviations from long-term measurement data were small. June temperatures, at 14.0 to 16.5 °C, were above the long-term mean values. Mean precipitation values were exceeded in most areas. In Vorpommern, in the area between Cape Arkona and Ueckermünde, extraordinarily large rainfalls were recorded. Sea surface temperatures in the Baltic corresponded to the long-term means. Nutrients were nearly depleted. Oxygen conditions in the coastal waters of Mecklenburg-Vorpommern were good.
The abundance of phytoplankton was relatively low. Dinoflagellates and diatoms had largely disappeared from the Baltic coasts of Schleswig-Holstein. The predominant plankton species were small flagellates. Off the coasts of Mecklenburg-Vorpommern, cryptoflagellates of the genus Rhodomonas prevailed, among others. Explosive growth of filamentous benthic algae repeatedly led to major pollution of beaches on the islands of Hiddensee and Rügen .