Thousands of dead fish were found floating on the banks of the Oder river, which runs through Germany and Poland, over the past weeks. Authorities haven’t yet provided any clear explanation about the causes of this environmental disaster and residents are being urged to stay away from the water. Experts warn it will take years for the river to recover, as speculations about illegal chemical dumping intensify.

The river runs from Czechia to the border between Poland and Germany before flowing into the Baltic Sea. At the end of July, it became clear that something was very wrong with the river. Polish anglers reported masses of dead fish near the town of Olawa, 300 kilometers away from the current fish die-off. The situation worsened from then on, with more dead fish found in the river at different spots.

Polish Prime Minister Mateusz Morawiecki said “everyone had initially thought that it was a local problem” but now admitted that the “scale of the disaster is very large.” He said, “huge amounts of chemical waste” were likely dumped into the river and offered a $220,000 reward to anyone who helps to track down those responsible for polluting.

Morawiecki fired the head of Poland’s national water management authority, Przemyslaw Daca, and the head of the general environmental inspectorate Michal Mistrzak, claiming both institutions should have reacted earlier. Poland has now assigned soldiers to help clean up and collect the dead fish from the river.

German officials have signaled that Poland failed to honor an international treaty by not notifying them immediately about the possible contamination of the river. Christopher Stolzenberg, a spokesperson for Germany’s Federal Environment Ministry, told reporters in Berlin that the chain of reporting created for such cases didn’t work.

Possible explanations

The German state of Brandenburg’s Environment ministry said an unknown and highly toxic substance in the Oder river was probably the cause of the mass die-off of fish. The ministry analyzed the river water and found evidence of “synthetic chemical substances” with toxic effects on fish – with no hint on how they entered the water.

“This fish death is atypical,” said Axel Vogel, environment minister for Brandenburg state, estimating that “undoubtedly tones” of fish have died. Fish death is sometimes often caused by disruptions of oxygen levels when water levels are low, he said. But this wasn’t the case here, with an increase in oxygen levels in the river for several days, Vogel said.

Poland had initially said the river could have been polluted by mercury, but this hasn’t been confirmed yet. Laboratory tests by Poland’s Environment ministry detected high levels of salinity in the water but no mercury. Tests were also done on seven species of dead fish and no mercury was found. Results of other substances are still pending.

Lawmaker Malgorzata Tracz from the Polish Green Party told DW that the Polish government failed to warn residents they shouldn’t touch the river’s water, estimating that about eight tons of fish were found near Olawa alone. “The problem is huge. It’s not something that can be ignored or that will be overcome on its own,” she added.

While not the main cause, drought in the region where the river flows is believed to have worsened the river’s condition and the extent of the fish die-offs. Piotr Nieznanski, the conservation policy director at WWF Poland, said in a statement the low water levels caused by the drought likely made conditions much more dangerous for the fish.

Ultimately, this environmental disaster showcases the importance of international collaborations — an earlier international alert signal could have helped avert some of the negative consequences.

“This ecological catastrophe would not have been of such magnitude if the German and Polish authorities had worked together more intensively,” Antje von Broock, managing director of the German Association for the Environment and Nature Conservation (BUND), said in a statement. “The fish kill is a symptom of decades of poor planning.”