dpatopbilder - 18.08.2022, Brandenburg, Lebus: Ein toter Blei liegt am frühen Morgen im flachen Wasser vom deutsch-polnischen Grenzfluss Oder. Seit mehren Tagen beschäftigt das massive Fischsterben im Fluss Oder die Behörden und Anwohner des Flusses in Deutschland und Polen. Foto: Patrick Pleul/dpa +++ dpa-Bildfunk +++

In the search for the causes of the mass death of fish in the Oder, there is a new suspicion: According to a report in the Polish newspaper “Gazeta Wyborcza”, the discharge of saline sewage from the KGHM Glogow mining operation in Upper Silesia between July 29th and August 10th contributed to the environmental catastrophe. The newspaper refers to the opposition MP Piotr Borys (Citizens’ Coalition).

So far, his accusation has not been that it is an illegal discharge. But that the state water authority should have banned the known discharge because of the low river level, because the salinity does not dilute quickly enough due to the lack of water.

The Polish government currently suspects a combination of several factors. The overall picture is still full of mysteries. The public prosecutor’s office is following up on several leads and is also investigating the initiation by KGHM. According to their own statements, the investigators have interviewed 228 witnesses and experts in the past four days and made site visits in twelve places.

Another farm in Olawa (Ohlau) east of Wrocław is also being examined, in the vicinity of which fishermen had already sighted many dead fish on July 26. Ohlau is 170 kilometers downstream from Glogau. The discharge of saline sewage in Glogau, which only began three days later, cannot have been the cause.

However, the saline sewage is not the only trace. According to the Polish government, toxic algae were discovered in the water samples examined from the Oder.

“After further investigations, the Institute for Inland Fisheries in Olsztyn found rare microorganisms, so-called golden algae, in water samples from the Oder,” said Environment Minister Anna Moskwa on Thursday. The bloom of these algae can cause the emergence of toxins that kill aquatic organisms such as fish and mussels, but are not harmful to humans.

On the German side, the poisonous species of algae Prymnesium parvum was recently identified in the Oder. Prymnesium parvum is also sometimes called golden alga, but this is not a biological term. Several species are so named because they shimmer golden. Neither the Institute for Inland Fisheries in Olsztyn nor the Polish Ministry of the Environment was initially able to find out the Latin name for the golden alga mentioned by Minister Moskva and whether it was the same type of algae that was discovered in Germany.