Algae bloom poisoned Oder River fish after salt level rise: Experts

Experts investigating what killed thousands of fish in the Oder River, which separates Germany and Poland, believe the spread of a massive bloom of algae may have been responsible, reported dpa.

Scientists from the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) say the algae bloom had already become apparent at the beginning of August, near the Polish town of Wroclaw.

Evaluations of satellite data had revealed a sudden increase in toxic chlorophyll concentrations along the entire course of the river from August 3-4, the IGB said on Thursday. These values - which are considered indicators of algal blooms - were also elevated from July 19-20.

The strong growth of the algae, which thrives in brackish water, is in turn due to an influx of salt into the river, researcher Tobias Goldhammer said. Where the salt came from is still unclear. Goldhammer said other factors also played a role, including low water levels and increased water temperature.

Whether the algal blooms of July and August are directly related cannot yet be conclusively assessed, according to the researchers.

What is clearly recognizable, however, is the very rapid spread of the bloom that followed, which covered almost the entire Oder from August 10 onwards. In the following two weeks, the chlorophyll concentrations decreased again, according to the data. It was not until the end of August that they reached medium levels again.