Between September 26 and 28, 2025, large numbers of dead fish washed up on the beaches of Nienhagen, Warnemünde, and Markgrafenheide. Back in January 2025, the IOW had installed measuring devices off Nienhagen that regularly record data on, for example, temperature, salinity, oxygen content, and turbidity of the water. One aim of the measurements is to investigate the development of oxygen-depleted areas in the still relatively unexplored shallow coastal waters of the Baltic Sea.