NewsWhat led to the death of fish in the...

What led to the death of fish in the Oder?

Created: 08/19/2022, 09:21 am

The cause of the massive fish kill in the Oder is still unclear. © Patrick Pleul/dpa

Why is the search for the cause of the great fish kill in the Oder so complicated? The culprit is difficult to identify. Authorities and researchers are looking for a needle in a haystack.

Potsdam/Cottbus – More than a week after the mass death of fish in the Oder became known, the cause of the biggest environmental disaster in Brandenburg for decades is still unclear. The State Office for the Environment and research institutes are investigating water and fish at high pressure. Authorities and scientists no longer grope in the dark. There are now various explanations for the death of the many fish.

Algae as a cause?

A toxic species of algae could be a key factor in fish kills, scientists say. A researcher at Berlin’s Leibniz Institute for Freshwater Ecology and Inland Fisheries identified the toxic species as a microalgae named Prymnesium parvum. According to the water ecologist Christian Wolter, it is known for occasionally leading to fish deaths. This is also confirmed by Jörg Oehlmann, head of the Aquatic Ecotoxicology department at the Goethe University in Frankfurt. However, it has not yet been proven that the alga’s poison is the reason for the fish die-off, only their mass development has been proven.

Why is there suddenly so much algae in the Oder?

According to the researchers, the algae species Prymnesium parvum actually only occurs in brackish water. It requires increased salinity, which does not normally exist on the affected Oder stretch. At the official measuring station of the State Office for the Environment in Frankfurt an der Oder, however, massively increased, unnatural salt loads were measured for around two weeks, which, according to the researchers, must have their origin upstream. According to the scientists, the mass growth of the algae also caused significantly increased measured values for oxygen, pH and chlorophyll. There are many barrages in the upper part of the Oder. Due to the low water there is currently hardly any water exchange there.

Other environmental influences

Climate change is stressing the sensitive ecosystem. For the researchers at the Berlin Leibniz Institute for Freshwater Ecology and Inland Fisheries, several harmful factors come together. Periods of drought and levels that are far too low, low oxygen levels and far too high water temperatures are “man-made” problems that increase the risk of environmental disasters, they say. At low tide, for example, harmful substances would be transported in a much smaller volume of water. This extreme condition stresses the fish. If other hazards such as toxic algal blooms or chemical contamination are added to the existing pollution, the entire ecosystem in water bodies can be destroyed, says researcher Jörg Oehlmann.

Difficult cause research

The Berlin-Brandenburg State Laboratory (LLBB) continues to examine water samples from different days and measuring points as well as fish. According to the Brandenburg Environment Ministry, the search for the cause of the fish kill is also difficult because there is no information from the Polish side, for example on possible discharges or specific reasons for the environmental disaster. Researchers say that research into the causes of the disaster by analyzing the substances in the Oder is a real Sisyphean task, since around 350,000 substances could potentially be present in a water sample – and even detailed diagnostics never cover all of them. The investigation could take weeks, according to the ecotoxicologist Oehlmann.

First results from Poland

Poland’s Environment Minister Anna Moskwa announced on Thursday evening that toxic algae had been discovered in water samples. These are so-called golden algae, which are deadly for fish and mussels. The Polish Ministry of the Environment and the responsible institute were initially unable to find out whether it was Prymnesium parvum.

Search for those responsible

The Polish government assumes an environmental sinner. “It is likely that a huge amount of chemical waste was dumped into the river, and with full knowledge of the risks and consequences,” Prime Minister Mateusz Morawiecki said last Friday (12 August). The Polish police have offered a reward of the equivalent of 210,000 euros for information on the perpetrator. The public prosecutor’s office has now heard more than 200 witnesses and completed twelve on-site visits on the Oder – so far there has not been a hot lead.

industry in sight

Investigators are also checking industrial plants near the river. In the days after the first indications of the fish kill, a paper mill in Olawa, Lower Silesia, south of Wrocław, was blamed on social media in Poland. The company denies. The plant had “neither anything to do with the environmental disaster on the Oder nor contributed in any way to it,” it said in a statement last week.

Experts such as chemistry professor Marcin Drag from the University of Applied Sciences in Wroclaw (Breslau) suspect that the river was contaminated with discharges from Silesian mining due to the high salt content. According to opposition MP Piotr Borys, a state-owned mining company regularly discharges saline wastewater from a huge retention basin near Glogow into the Oder – but it also has the approval of the water authority to do so. dpa

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