It is estimated that around 100 tons of dead fish have drifted down the Oder so far.

The first larger quantities of fish carcasses were found south of Breslau at the end of July, and the first finds in Germany were made near Frankfurt an der Oder on August 9th.

There, as early as August 7th, there were noticeable changes in some parameters, for example the pH value of the river water rose significantly, i.e. it became more alkaline.

It is also unclear whether the high water temperatures or the low water levels have anything to do with the phenomenon.

Ulf von Rauchhaupt

Editor in the “Science” section of the Frankfurter Allgemeine Sunday newspaper.

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On Wednesday, researchers discovered a widespread alga in the Oder that could be responsible for the mass extinction.

His colleague Jan Köhler identified the Prymnesium parvum “under the microscope without a doubt,” said fish ecologist Christian Wolter of the FAZ. The alga is known for being able to release toxins.

Whether this happened in this case has not yet been proven.

“We have to prove the poison in a water sample.

It's the colleagues' turn," said researchers at the Berlin Leibniz Institute for Freshwater Ecology and Inland Fisheries.

Fortunately, the poison does not occur frequently, which is precisely why the analysis is difficult.

Some indications support the theory: The algae found normally live in brackish water, they like saline habitats.

Around August 7, the electrical conductivity of the water also increased dramatically.

This indicates that a saline substance had been introduced into the river.

Salts are ions, they are measured as conductivity in the water.

"The values ​​were twice as high as normal," said Wolter.

Without the salt, the algae could not spread so much and could not form poison.

Wolter does not assume that the substance introduced was an accident.

The conductivity of the water is now slowly sinking again, but the data shows that the substance must have flowed into the Oder for about two weeks.

Algae causes cloudiness

The algae were able to grow particularly well due to the low water and the sun.

The higher oxygen content of the water also makes sense, since the algae produce oxygen.

On the other hand, nitrate nitrogen is a plant building block that the algae literally absorb, the value had dropped sharply around August 7th.

The increased turbidity in the water can also be explained by the algae.

If the alga has actually produced poison, it attacks the fish's gills and destroys them.

Mussels also died in the environmental disaster.

The toxin immediately dissolves soft tissue, Wolter said.

The dead mussels found would no longer have had the so-called byssus threads that normally give them adhesion.

If mussels were to die normally, the byssus threads would still be attached to them.

Laboratories in Germany and Poland are currently examining cadavers and river water for around 300 different chemical substances.

However, the current data situation is still incomplete, said Jörg Oehlmann, head of the Aquatic Ecotoxicology department at the Institute for Ecology at the University of Frankfurt am Main, the Science Media Center Germany.

"Specifically, even basic data is missing, such as the levels of total phosphorus, orthophosphate and ammonium in the water.

In this respect, valuation is subject to precisely these uncertainties.”