July was summer-like warm and dry. Sea surface temperatures were up to 3.4 K above average (July: 18,6 - 19,9 °C). The typical seasonal exhaustion of nutrients was observed.
At the end of July oxygen levels reached up to 70 % saturation. In spite of the warm weather oxygen consumption in the bottom water was not critical until now.
Unusual algal development was not observed. Plankton showed a wide variety of species. Low cell concentrations of diatoms, flagellates and ciliates, with diatoms (Rhizosolenia imbricata) prevailing, were found. The light-emitting Noctiluca scintillans was only abundant in some places. Off Helgoland there was
reddish water colouring caused by Myrionecta rubra. In the Northern Sylt Wadden See, a second bloom of Phaeocystis globosa reached a peak in mid-July. Potentially toxic Dinophysis were found at low concentrations.
An increase of green algae in the coastal waters of Lower-Saxony was observed in July.
In July oxygen in the water surface layer of the Pommeranian Bight was high with levels above 9 mg/L. The bottom water concentrations gradually decreased. In the bottom water of the south eastern Gotland Basin oxygen was very low. Hydrogen sulfide was found in the deep water of large areas of the Baltic Sea.
Until mid-July an increase of cell number, especially of summer-like dinoflagellates Prorocentrum minimum and Heterocapsa triquetra was observed. High concentrations of blue-green algae were abundant in the Baltic Proper. In front of Heiligenhafen and Puttgarden and in the Bay of Lübeck, a surface accumulation was noticed in the water for a short time. Potentially toxic Nodularia spumigena and Anabaena sp. were found in the floating flakes but heavy winds dispersed them in the water column during the week end. Out in the open sea at 15 m depth the potentially toxic dinoflagellate Dinophysis norvegica occured in relatively high numbers.
In the eastern coastal waters of Rügen a mass development of filamentous algae continued. Large amounts of filamentous brown algae were seen in the open sea; large lumps floated towards the Swedish coast.