The German side submitted its report on the fish kill in the Oder one day after the authorities in Poland. The reason for the disaster was the salt content in the river, which is actually more typical of brackish water. But only Poland could determine the cause.
According to the federal government, an algal bloom triggered by “unnaturally high” salt concentrations is the most likely cause of the massive fish kill in the Oder this summer. According to the report by the Federal Environment Ministry and the Federal Environment Agency, this is the “most plausible hypothesis”. The toxins produced by the alga Prymnesium parvum triggered the death of fish in the river, which was already “stressed” by the heat.
According to their own statements, the German experts could not determine the cause of the salt concentration. The answer to this question had to remain open “due to a lack of available information”, explained the Ministry of the Environment and the Federal Environment Agency. Federal Environment Minister Steffi Lemke. It is now also important to analyze the damage to the environment and to regenerate the river.
According to the report, the rapid multiplication of the toxin-producing alga is documented by water samples and satellite images. It is actually found in brackish water on seacoasts where salt and fresh water mix. Accordingly, the rapidly increasing salt concentration of the German-Polish border river and the strong summer sunshine favored their growth. However, it also remains unclear how the algae species found its way up the Oder. According to the German authorities, contamination of the river with heavy metals or chemicals was classified as “less likely” as a cause. The Polish investigations must now clarify why the salt concentration has risen so much.
The fish kill had led to massive upsets between Germany and Poland, partly because of the lack of warnings from neighboring countries. The day before, Polish authorities had published a preliminary investigation report. According to this, too, the algal bloom was responsible for the fish kill. The Polish authorities, on the other hand, ruled out industrial wastewater as a cause. The environmental organization Greenpeace, among others, suspects salt discharges from the Polish mining industry as the trigger.
A spokesman for the Federal Ministry for the Environment emphasized that the determination of the causes could not be further advanced from Germany due to a lack of data. It is “a good signal” that the Polish side announced further investigations when presenting their interim report. Germany is dependent on the neighboring country, he said.
The fish kill first appeared in the region around the Polish city of Wroclaw in late July and continued upriver in the weeks that followed. The phenomenon was first noticed on the German side in mid-August and triggered emergency measures. A warning was given against contact with the river water.
Lemke announced aid for the affected regions and the renaturation of the Oder. At the same time, she again called for the Polish side to abandon the measures to expand the Oder, which had long been criticized by the German side. She also referred to possible consequences in other rivers.