Compared to the long-term monthly means, July and August were too warm, with an above-average number of sunshine hours, and mostly too dry. Sea surface temperatures reached in August, maximum temperatures around 22 °C in the North Sea and up to 23 °C in the Baltic Sea. Oxygen in the surface layer almost reached the saturation level of 100 %. Near the bottom, concentrations of 60 - 90 % were measured. The oxygen concentration in the surface layer of the Baltic Sea was normal. In the near-shore area of the Pomeranian Bight, an extreme oxygen deficiency was observed in the water body. An intensive rotten odour above the whole water surface indicated the presence of hydrogen sulfide. In the Gotland and Bornholm Basins, oxygen saturation was below 10 %. Hydrogen sulfide was found in the eastern Gotland Basin. Nutrient concentrations were low, in line with the season.
In the North Sea, summer plankton had the usual composition of small diatoms, small flagellates, and Ceratium species. In the North Sylt Wadden Sea, an unusual mass development of the tubular diatom Rhizosolenia imbricata was observed. The light-emitting Noctiluca scintillans was abundant in some places. The abundance of the foam-producing alga Phaeocystis globosa decreased in August. An upward trend was observed for cod stocks.
In the entire Baltic region, calm and warmer than usual weather favoured the development of high concentrations of filamentous blue-green algae, such as Aphanizomenon sp., Nodularia spumigena (potentially toxic), and Anabaena spp. Blue-green algae were also observed east of Fehmarn and in the Bay of Lübeck, but the algal mats did not reach the beaches at any time. On beaches of the Danish east coast and at Swedish and Finnish beaches, people were warned against bathing to avoid skin irritation or gastrointestinal infection.The 1995 flounder year-class hardly reached average size, like the 1993 and 1994 year-classes. The 1996 cod year-class failed to reach the above-average size of the 1994 year class. Dab stocks in the Mecklenburg Bight continued to decline.
First data on the impact of the Oder flood on the Baltic Sea are available. German and foreign institutes carried out permanent environmental monitoring of the Oder river, Haff area, and a large area off the Pomeranian Baltic coast. Evidence for input by the Oder flood could be obtained near the coast by measuring elevated nutrient and pollutant