30.08.2022, Brandenburg, Brieskow-Finkenheerd: Mehrere verschiedene Arten von lebenden Fischen sind in einem Kescher von Fischereiwissenschaftlern vom IGB Leibniz-Institut für Gewässerökologie und Binnenfischerei zu sehen. Wissenschaftler vom IGB waren am Vormittag auf dem deutsch-polnischen Grenzfluss Oder unterwegs, um hier lebende Fische zu fangen. Die Umweltkatastrophe am Fluss Oder beschäftigt weiterhin viele Wissenschaftler. Derzeit untersuchen die Mitarbeiter vom IGB die lebenden Fische im Fluss Oder. Foto: Patrick Pleul/dpa +++ dpa-Bildfunk +++

After the massive death of fish in the Oder, hopeful news comes from the river: According to the professional fishermen, the stock is recovering noticeably. The result of two studies in the Oder is that the fish are doing surprisingly well, according to the Brandenburg-Berlin State Fishing Association on Tuesday.

The exact cause of the environmental disaster is still unclear. Experts assume that a high salinity in the river is a major reason, combined with low water, high temperatures and a toxic species of algae.

According to scientists, however, it is still unclear how quickly the poison of the algae can break down. The association Forum Natur meanwhile warns against distracting people from the search for environmental sinners. The catastrophe was man-made.

“The Oder is recovering noticeably. You can see living mussels and snails and fish that are vital,” said Lars Dettmann, Managing Director of the Brandenburg-Berlin State Fishing Association on Tuesday. Together with the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB), he was on a stretch of river near Brieskow-Finkenheerd near Frankfurt (Oder) to observe the fish population during a second sampling.

According to Dettmann, in a first investigation eleven days ago, 14 species were discovered among 550 healthy fish, including perch, small zander, pike and loach. The latter is a very sensitive fish species.

A second sampling this Tuesday also gave a preliminary positive picture. More healthy fish species have been added, a final evaluation will follow, according to Dettmann. Apparently the algae toxin did not reach everyone.

Since the beginning of August, tons of dead fish have been recovered from the German-Polish border river. Federal Environment Minister Steffi Lemke (Greens) announced on Monday that several hundred chemical substances could be responsible for the environmental disaster. The exact cause of the environmental disaster is still unclear.

In the meantime, the water of the Oder has risen by about a meter, according to the managing director of the state fishing association. “The Oder is recovering, but it will take years for what broke to heal,” Dettmann estimated.

According to the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB), it is not yet possible to say how quickly the toxin of the algae breaks down in the river. This is still being investigated by other scientists.

So far, there have been few studies in which the degradation of the toxin by light (photolysis) has been demonstrated, according to the institute. The breakdown of the algal toxin is a combination of various factors such as light intensity, properties of the water and the type of toxin.

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Meanwhile, the managing director of the association Forum Natur, Sabine Buder, warned against neglecting the search for the cause of the environmental disaster. The biological cause of the algae toxin is a “feel good argument”.

“What has not been reconstructed to this day is who was the person who introduced the substances,” said Buder. With a view to the German-Polish meeting in Bad Saarow, it is irritating that this point no longer seems to be relevant, she criticized.

A group of German and Polish experts is to present results on the cause of the massive fish kill in the Oder by September 30th. This was announced by Federal Environment Minister Steffi Lemke and her Polish counterpart Anna Moskwa on Monday in Bad Saarow at the meeting of the German-Polish Environment Council.

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In connection with the fish kill in the Oder, Poland’s water authority claims to have discovered 282 wastewater discharges without a current water permit. The Polish police offered a reward of the equivalent of 210,000 euros for information on the perpetrators.