The fish that perished by the ton in the Oder in August died from a toxic algae that was able to multiply rapidly due to increased salt concentrations in the river. This is now confirmed by studies by the Federal Environment Agency and the environmental organization Greenpeace. The latter found additional evidence of uncontrolled discharges by the Polish mining industry, which are a possible cause of the high salt levels, Greenpeace spokesmen said.
In August 2022, tons of dead fish washed up on the banks of the Oder, which flows from the Czech Republic via Poland and Germany into the Baltic Sea. The first investigations that were initiated to clarify the environmental catastrophe quickly identified the increased growth of a toxic alga as the cause of death: the microalgae Prymnesium parvum produces a strong toxin that is particularly life-threatening for mussels, amphibians and fish. But what conditions favored the rapid growth of the toxic alga? And what was the reason for the development?
Expert group confirms high salt levels
In mid-August, German Environment Minister Steffi Lemke and her Polish counterpart, Anna Moskwa, set up a group of experts to clarify the causes of the Oder disaster. The Federal Environment Agency, which provides the German experts in this group, evaluated numerous water samples and satellite images in the course of the search for the cause and came to the conclusion that a rapidly increasing salt concentration in the Oder and solar radiation had favored the rapid growth of the brackish water algae Prymnesium parvum.
“The fish kill in the Oder is a serious environmental catastrophe. It was caused by human activities, which is a central finding of the investigations: According to the experts, salt discharges are the cause of the fish kill,” reports Lemke. However, due to a lack of available information, the experts had to leave open who or what was responsible for the salt discharges that led to the unnaturally high salinity. In addition, it is still unclear how the brackish water algae, which normally occurs in coastal waters, found their way into the Oder.
mining industry responsible?
A German-Polish team from the environmental organization Greenpeace came to similar conclusions. At the end of August, the environmentalists took seventeen water samples between Schwedt in Brandenburg and the Polish-Czech border along a river length of about 550 kilometers, which confirmed the increased salt concentrations. Their analyzes provided additional indications of the mining industry as a possible cause. According to the Greenpeace spokesman, the highest salt levels were found in a retention basin owned by the mining company KGHM in Gmina Polkowice. The salinity there was 40 times higher than the values recommended for fresh water. Also noticeable were high salt levels upstream on the Gliwice Canal, through which other mines discharge their waste water into the Oder.
According to the environmentalists, the Oder is also a heavily polluted river because the water quality and discharge operations are not continuously monitored on the Polish side. “While live monitoring registers pollution in real time in Germany, this form of monitoring is missing here. This means that after the authorities have closed, there are no more checks. At night, anything is possible for someone who wants to illegally dump their waste in the river,” says Marek Jozefiak, spokesman for Greenpeace Poland.
The future of the Oder
Federal Environment Minister Lemke also sees room for improvement in the control of the inflows on the German and Polish side: "The revision of the warning and alarm plan for the Oder has already begun. It is also clear that fish kills are not just a problem in the Oder. In view of the climate crisis, we must seriously examine what we can still expect from our rivers in the future. We have to check and reduce the discharge of substances, for example from sewage treatment plants, into rivers". Equally important is the renaturation of the Oder as a habitat for rare species and as a source of important ecosystem services for local people. The Federal Environment Ministry is therefore currently driving a project to record the damage to the ecosystem, monitor natural regeneration and lay the foundations for effective renaturation measures.
Source: Federal Ministry for the Environment, Greenpeace Germany