Even if the question of the origin of the fish die-off in the Oder has not yet been finally clarified, there are increasing indications that toxic algae play an important role. They spread very quickly in Poland at the beginning of August, as satellite data shows.
According to the Brandenburg Environment Ministry, the exact cause of the fish kill in the Oder has not yet been finally clarified. The final report by a German-Polish group of experts on the causes should be available by the end of September. Scientists assume that high salinity in the river is a major reason, combined with low water, high temperatures and a toxic species of algae.
The Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB) gained further insights into the toxic species of algae. According to the scientists, the spread of a massive algal bloom in the river was already evident in early August near Wroclaw (Poland). Evaluations of satellite data from August 3rd to 4th showed a sudden increase in chlorophyll concentrations in the entire course of the river, as the IGB further announced. These are considered indicators of algal blooms. These values were also increased from July 19th to 20th.
The experts at the Leibniz Institute for Freshwater Ecology and Inland Fisheries see clear signs that a toxic alga is to blame for the massive fish deaths. Researcher Tobias Goldhammer said that the strong growth of the algae, which actually thrives in brackish water, is due to salt being introduced into the river. Where the salt comes from is still unclear.
According to the researchers, it is not yet possible to conclusively assess whether the algal blooms in July and August are directly related. What is clearly recognizable, however, is the very rapid spread of the bloom that followed and which from August 10th covered almost the entire Oder. In the following two weeks, the chlorophyll concentrations reportedly decreased again. It was only at the end of August that they returned to the medium level.
After the massive fish die-off, 19 healthy fish species have now been detected again during sampling in a section of the Oder in Brieskow-Finkenheerd near Frankfurt (Oder). That said the scientist at the Institute for Inland Fisheries in Potsdam-Sacrow (IfB), Daniel Hühn. The more than 1,800 fish caught included everything from juvenile fish to perennial fish.
However, the random sample only gives you a fraction of the fish that are actually in the Oder, the scientist explained. They were caught with electrofishing, this method is limited to shallow water and stagnant water. During the first sampling on August 19, according to the state fishing association, 14 species were discovered among 550 healthy fish, including perch, small zander, pike and wolffish.
