The Oder River fish die-off has many causes, say early reports from scientists.

In late July and early August of 2022, thousands of tons of dead fish choked the surface of the Oder River, which forms most of the border between Germany and Poland. Weeks later, no firm cause has yet been turned up.

“The search for the causes of the fish die-off in the Oder still haven’t been completed,” said Andreas Kuebler, spokesman for Germany’s Environment Ministry. “So far we have several organic and inorganic substances that could be responsible.”

“It seems to be a cocktail of chemicals,” he told reporters in Berlin. “According to our information so far, none of these substances alone led to the fish die-off. It must still be assumed that this could be a multi-causal incident.”

One possible culprit he mentioned is an algae bloom producing toxins, one that would have been caused by high salt levels in the water from industrial discharge.

Polish Environment Minister Anna Moskwa accused Germany of spreading “fake news” about pesticides in the water, even though the Polish prime minister is calling the die-off an environmental catastrophe.

“In Poland, the substance is tested and detected below the quantification threshold, that is, it has no effect on fish and other species,” she tweeted, in Polish.

The dead fish, floating in thick drifts on the Oder River, were first noticed by river fisherman in Poland in July, who alerted the Polish government. Word was not sent to German officials for over two weeks.

Kuebler, who has not assigned blame to any particular factor, says he’s saddened by the defensiveness out of Poland.

Poland has removed over 100 tonnes of dead fish from the Oder River, to prevent the spread of disease and hopefully help reduce the concentration of whatever factor has caused this mass death event.

Photo: Dead fish floating atop a river of polluted water. Credit: Shutterstock