16.08.2022, Brandenburg, Schwedt: Andreas Hein, Ranger bei der Naturwacht Brandenburg, steht mit Schutzbekleidung im deutsch-polnischen Grenzfluss Westoder, nahe dem Abzweig vom Hauptfluss Oder und holt mit einem Kescher tote Fische aus dem Wasser. Mitarbeiter vom Nationalpark Unteres Odertal, Ranger der Naturwacht Brandenburg, Mitarbeiter vom Landkreis Uckermark und freiwillige Helfer sind seit den Morgenstunden mit dem einsammeln von toten Fischen im Gebiet des Nationalparks Unteres Odertal beschäftigt. Seit mehren Tagen beschäftigt das massive Fischsterben im Fluss Oder die Behörden und Anwohner des Flusses in Deutschland und Polen. Das Fischsterben in der Oder ist nach Angaben der polnischen Umweltschutzbehörde wahrscheinlich von einer Wasserverschmutzung durch die Industrie ausgelöst worden. Foto: Patrick Pleul/dpa +++ dpa-Bildfunk +++

From the point of view of the Leibniz Institute for Aquatic Ecology, the riddle surrounding the massive death of fish in the Oder includes indications that the animals died from a poison produced by algae. The strong growth of the algae, which actually thrives in brackish water, is in turn due to salt input into the river, said researcher Tobias Goldhammer on Monday of the German Press Agency. “That is our currently most likely hypothesis.”

Last week, the Berlin institute pointed out the strong growth of the algae species Prymnesium parvum, which can form a poison that is deadly for fish. At the weekend, the institute added that this poison had actually been detected in the water of the Oder. In addition, satellite data would have shown a massive algal bloom in the Oder.

Initial tests on fish eggs with the Oder water had confirmed the deadly effect, Goldhammer told the dpa. “In the chain of evidence, it is very likely that this algal bloom is the cause of this fish kill.” However, this has not yet been definitively proven.

It is also important that the algal bloom is not a natural event, but is due to human influences, namely the increased salt load in the river water. It is currently not possible to prove where the salt came from. Other factors also likely played a role, including low water and increased water temperature, Goldhammer said. He is a research group leader in the Department of Ecohydrology and Biogeochemistry at the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB).

Meanwhile, the federal government has rejected Polish allegations in connection with the fish kill in the Oder. “We regret that this assessment came from Poland,” said a spokesman for the Federal Ministry for the Environment on Monday in Berlin, referring to the accusation from Warsaw that Germany was spreading “fake news”. The search for the causes of the fish kill in the Oder is still not complete.

There are now several organic and inorganic substances that could be responsible, the spokesman said. “It really seems to be a chemical cocktail. According to our current knowledge, none of these substances alone caused the fish to die.” It could be a “multi-causal event”.

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“But no one in Germany and at no time claimed that the pesticides alone were the cause of the fish kills. It is regrettable that the Polish Ministry of the Environment now took the corresponding laboratory results as a way of assigning blame.”

The German-Polish expert group set up a week ago met for the first time on Monday and exchanged laboratory values ​​and test results. It is made up of experts from the federal government and the federal states concerned, as well as from the Polish authorities at national and regional level. The Federal Environment Agency is in charge on the German side. The ministry spokesman had previously expressed the hope that a “possible disagreement” would be cleared up when the data were discussed in the working group.

Poland’s Environment Minister Anna Moskwa wrote on Twitter on Saturday evening: “Warning, another fake news is being spread in Germany!!! pesticides and herbicides. In Poland, the substance was tested and found below the limit of quantification, i.e. H. with no impact on fish or other animals, and no connection to fish kills.”

The Polish government also criticized the fact that German authorities had set up only a few oil barriers to catch the masses of fish that had died in the Oder. “This really raises the question of why we have already been able to erect 29 oil barriers in which fish are caught on the Polish side, while only three such barriers have been erected on the German side, despite our requests,” said Deputy Foreign Minister Szymon Szynkowski vel Sek on Monday the public broadcaster Polskie Radio. The Polish fire brigade is also willing to borrow these barriers or set them up on the German side. Boom booms are deployed in the river to catch and recover dead fish before they drift further downstream.

[Read more at Tagesspiegel Plus: “There was total silence”: Or catastrophe arouses incomprehension, disappointment and anger at the authorities]

In the past few days, masses of dead fish have been discovered and collected in the Oder on the Polish and German side. On the German side, the massive death of fish in the Oder became known on August 9th. In Poland, on the other hand, there were first indications of fish carcasses in the border river at the end of July. The German authorities accuse the Polish side of informing them too late, making it difficult to find the cause.