A sudden increase in salinity in the Oder River has led to the appearance of toxic algae and caused the death of hundreds of tons of fish this summer, BTA reports, citing a report by German experts.

"The most likely cause of the fish die-off in the Oder is a sudden increase in salinity, which, together with other factors, has led to a massive spread of saltwater algae that are toxic to them," said the report presented on Friday by the German Ministry of environment.

Prymnesium parvum algae "produces a toxic substance that is lethal to fish and other aquatic organisms," the document also said.

Studies in a German lagoon have not provided an explanation for the death of tons of fish in the Oder River

They are believed to have appeared as a result of an unexplained concentration of salt and caused the death of about 300 tons of fish this summer in the Oder River, which separates Germany and Poland.

According to the report, "experts should have left open the question of what caused this unusually high salinity."

"It is also not known how the saltwater algae, which are usually found in coastal waters, ended up in the interior of the country," the experts added in a statement published by the environment ministry.

On Thursday, Polish authorities also indicated in a preliminary report the role of algae in this "hecatomb" and ruled out any industrial cause for the sudden deterioration of the river water.

However, according to German Environment Minister Steffi Lemke, this "serious ecological disaster" is undoubtedly "caused by human activity". 

The reasons for the high salinity, the "main trigger" of the ecological disaster, "are not clear," the German experts wrote.

According to them, "multi-causal mechanisms of action" caused the fish die-off. 

Experts also believe that the conditions necessary for algae to spread are present in the Oder in summer, including low flow and water levels. 

The disaster somewhat strained relations between Berlin and Warsaw.

Germany accused Poland of being late in informing it about the extent of the pollution.

The first reports of mass fish kills in the Oder came from Polish residents and fishermen on July 28.

In recent years, the Oder has been known as a relatively clean river in which about 40 species of fish live.

dead fish

Oder river