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Lack of oxygen causes fish deaths in the Baltic Sea – all clear!
Rostock reports fish deaths due to lack of oxygen. The cause is environmental influences. Swimming and fishing are safe again.
Lack of oxygen causes fish deaths in the Baltic Sea – all clear!
In the Baltic Sea near Rostock there were massive fish deaths on the beaches of Nienhagen, Warnemünde and Markgrafenheide. Worrying scenes unfolded last weekend as scores of dead flounder, plaice and cod washed up on shores. On October 1, 2025, the Rostock town hall gave the all-clear after comprehensive scientific investigations into the causes of the carcass materials had been completed. The researchers primarily blamed a lack of oxygen caused by the upwelling effect. Strong offshore winds push the surface water away and oxygen-poor deep water flows upwards, causing bottom-dwelling fish species to struggle to breathe, reports geo.de.
The exact circumstances were intensively investigated. In total, the scientists from the State Office for Agriculture, Food Safety and Fisheries (LALLF) checked around 420 different pollutants. Interestingly, no harmful substances such as herbicides, pesticides or pathological microorganisms were found. An epidemic could also be ruled out. This underlines that the quality of the fishing product in the affected region is harmless. The Rostock Veterinary and Food Inspection Office has therefore allowed fishing for food production again, which is good news, especially for anglers.
Environmental factors and human influences
Environment Minister Till Backhaus made it clear that the lack of oxygen was man-made. Nutrient overload from agriculture and the effects of climate change lead to high biomass production, especially from algae. This high biomass consumes oxygen during microbiological degradation, which increases the critical situation in the Baltic Sea. “Such upwelling events and associated fish deaths can occur more often in the autumn months,” warns Backhaus, as in a report by sueddeutsche.de.
Rostock's health department initially recommended being careful when bathing. This warning has now been lifted now that the scientific results are available. Once again nothing stands in the way of a carefree day on the beach. The situation once again underlines the challenge facing the Baltic Sea and that environmental protection and fisheries management must go hand in hand.
This is a relief for local fishermen and anglers, as they can now eat their catches again without hesitation. But the warning remains: such incidents could occur more frequently in the future if nothing is done to reduce nutrient pollution in the Baltic Sea.