After massive criticism from Germany, the Polish government announced the first results on the causes of fish deaths in the Oder: A toxic species of algae had been detected. It is still unclear whether a salt discharge led to the propagation of the plants.
According to the Polish government, toxic algae were discovered in the water samples examined from the Oder. "Following 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. 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. Moskva said additional research had confirmed that a golden algal bloom had occurred in the Oder. The cause of the algae bloom is still under investigation.
The death of fish in the Oder has been worrying people who live on the river in Poland and Germany for days. According to the Ministry of the Environment in Brandenburg, their own warning and reporting chains are currently being checked. Among other things, it is about whether the existing measurement practice needs to be reassessed and adjusted, it said in the afternoon. The "Spiegel" had previously reported that the State Office for the Environment had already registered at the beginning of August that the water of the Oder had changed. The Brandenburg authorities had remained inactive, the report said, among other things.
"From the values measured up to that point in the automated measuring point in Frankfurt (Oder) alone, a fish kill could not be assumed," said a ministry spokeswoman. According to her, there had already been significantly high values in the past, which indicated salt loads, but would not have caused fish to die in the Oder. According to the ministry, there have been increased salt concentrations in the Oder for many decades.
The automatic measuring station in Frankfurt (Oder) recorded an increase in the curves for the parameters conductivity, oxygen content and chlorophyll from August 7th to 8th. According to the Ministry of the Environment, these were not yet capable of interpretation on their own. In particular, with a view to the fact that the Oder is already under stress due to the extremely low water, intense heat and high water temperatures, they did not provide any more direct information. However, the values continued to be observed.
According to an international agreement, the Polish side should have triggered the reporting system applicable to the Oder when mass fish deaths became known there. The ministry spokeswoman made it clear that Poland has not done so to this day. Better precautions could have been taken with a warning, such as setting up barriers. Now the state authorities are constantly supplying data to the Polish side, but nothing comes from there, reported Zelt. So far, the Ministry has only been informed by the Polish authorities that water samples have been taken and fish are being examined.
The aquatic ecologist Christian Wolter had already named the toxic algae as a possible cause of fish deaths on Wednesday: "The species is known for the fact that fish die occasionally". However, it is still unclear whether the toxin of the algae is the reason for the fish deaths in the Oder. The researcher at the Berlin Leibniz Institute for Freshwater Ecology and Inland Fisheries emphasized whether it produced toxins in this case. He spoke of a massive algal bloom with 200 micrograms per liter and more than 100,000 cells per milliliter of water and suspected salt discharge into the river as the trigger.
Yet another expert saw the proliferation of certain algae as a key factor. "For me, it is relatively plausible that this massive proliferation of algae has occurred - and in connection with this, the release of toxic substances produced by these algae is well documented," said Jörg Oehlmann, head of the Aquatic Ecotoxicology department from the Goethe University in Frankfurt. "We also know that these toxins can cause such fish kills even at relatively low concentrations." Whether these are ultimately blue-green algae or the toxic species of algae Prymnesium parvum, which was last identified in the Oder, remains to be clarified, says Oehlmann.
According to Oehlmann, the phenomenon of mass algae growth is either due to the high temperatures and strong solar radiation or the man-made introduction of certain substances. Research into the causes of the catastrophe by analyzing the substances in the Oder is now a real Sisyphean task, since around 350,000 substances could potentially be present in a water sample - and even detailed diagnostics never cover them all. "It can take weeks before the substance behind it has actually been identified and can be named," said Oehlmann.
According to its own statements, the EU Commission is extremely concerned and is pushing for results in the investigations into fish deaths in the Oder. "It is extremely important and urgent to determine the cause and take the appropriate measures downstream," said a spokesman for the Brussels authority. "The sooner we can identify the cause of this ecological catastrophe, the sooner we can begin to manage and limit the wider impacts on wildlife, fisheries, agriculture and recreation," the spokesman said.
