Origins of mass die-off of fish in the Oder River still unknown

Origins of mass die-off of fish in the Oder River still unknown

Disclaimer: An updated and more in-depth version of this article will appear in the September issue of The Conservation & Livelihoods Digest.


In late July 2022, things started to change in the Oder River – the border river between Germany and Poland. Residents living along the river banks in the Polish city of Oława started to notice large numbers of dead fish floating in the low waters of the Oder. As such, this is nothing unusual. After all, water levels have been dropping due to the heat wave that has been hitting Central Europe for a few weeks now. But also on the German side, fishers started to notice what they only knew from disaster movies: hundreds, thousands of dead fish started to appear, which are more than usual. As a consequence, they alerted the authorities that things are not what they should be in the Oder.

The main authority for the Oder on the German side is the Environment Agency of Brandenburg (Landeamt für Umwelt Brandenburg, LfU). LfU operates several stations along the river, which monitor water quality. From 1 August onward, these stations picked up a rather sudden increase in conductibility, which is an indicator of the water’s salinity. Between 1-6 August, salinity levels rose from 1300 MilliSiemens per centimetre to more than 2000 MilliSiemens per centimetre – even going beyond what could be displayed on LfU computers. As Der Spiegel reports, however, the LfU merely observed and did not react (Kollenbroich, Merlot & Schrader, 2022).

Apart from salinity, also oxygen levels and PH-levels rose dramatically while the cloudiness of the water and UV absorption – a sum parameter for specific dissolved organic substances – increased. Lastly, levels of nitrate-nitrogen dropped, which could be an indicator for increased algal bloom.

The devastating result of these drastic changes has thus far been: More than 30 tonnes of dead fish taken out of the river by German authorities and more than 100 tonnes of dead fish taken by Polish authorities. At least more than 500km of the river are now dead waters. Four Polish provinces – Opolskie, Dolnośląskie, Lubuskie and Zachodniopomorskie – and the German province of Brandenburg are directly affected by this disaster. Now it is feared that the mass die-off expands into other waters since the Oder discharges into the Szczecin Lagoon, thus also affecting Mecklenburg-Vorpommern, before flowing into the Baltic Sea. Thus far, however, this has not occurred.

Affected regions by the Oder River mass die-off © Nikolas Sellheim 2022.

The question remains, what has caused this drastic change in water quality within just a few days leading to one of the most devastating fish mass die-offs in the history of the Oder?

Theories for the mass die-off

Up to this day it remains unclear what has caused this event. The original theory circled around a possible industrial accident or deliberate pollution. In the focus of attention were levels of mercury which could have caused such drastic changes within a short period of time. Polish and German authorities investigated this issue and more than 200 individuals were interrogated. The result was, however, that mercury levels were still in the norm while there are thus far no indications for an accident or deliberate acts of pollution.

That said, it is not impossible that some form of chemical might have caused this environmental disaster. After all, it depends on the way laboratories work. When looking for a known chemical, this chemical is rather easy to spot. But the search for an unknown chemical as a cause might prove significantly more difficult: once released into the river, it might have caused a chain reaction due to the interaction with the river’s flora and fauna – only then exposing its deadly character. Another challenge to find it is that it might have changed its chemical structure due to its exposure to oxygen or sunlight. Consequently, even though nothing has been found yet, this does not mean that this possibility can be ruled out.

This is especially the case since Poland’s Prime Minister Mateusz Morawiecki reported of possible environmental crimes, i.e. the release of large amounts of chemicals into the Oder close to the city of Opole. This report, however, came much too late and he was criticised for not having informed German authorities about this issue. He, in turn, reported that the the information about the river’s changes had reached him only by 9 or 10 August. As a consequence, he relieved the leaders of the water and environmental agencies of their duties. Even though earlier informing the German authorities would not not have prevented the spread of the toxin, it might have helped to coordinate cleaning efforts better in order to slow down the spread within the food chain.

Despite the still unknown cause for the mass die-off, it appears as if a yet unknown type of algae may be responsible. Researchers from the Berlin-based Leibniz Institute for Water Ecology and Freshwater Fisheries (IGB) have found a high concentration of an algae that emits a type of toxin which is extremely poisonous for fish. Although the type appears to be primarily occurring in brackish water, the high salinity associated with the high levels of oxygen point into the direction of the algae itself having caused the problems.

This leaves the question of why the level of salinity has increased so dramatically. Researchers from the IGB consider wastewater from Polish potash mining as having cause the increase in salt. Since this has been ongoing for a rather long time, the problem can indeed be considered an anthropogenically caused environmental disaster. Despite these indications, the theory has not yet been proven.

The way forward

The search for the origins of the disaster are still ongoing while fears of a spread of the die-off have prompted close monitoring of the Sczeczin Lagoon at the Oder’s river mouth. As of the time of writing, no fish die-off can be noted there. But in light of the transboundary nature of the catastrophe and the lack of information exchange at its early stages, the European Commission has offered support as regards expertise and information. Whether the cause will ever be found remains to be seen, but it remains imperative that environmental authorities closely cooperate in order to contain the damage as much as possible.

The Oder River in data

Length: 866 km to Szczecin
Source: Close to Kozlov în Czech Republic
River mouth: Swinemünde in the Szczecin Lagoon as well as Usedom and Wolin
Course: Czech Republic, Poland, German-Polish border area
Border river between Germany and Poland: 179 km
Navigable kilometers: 717 km


Kollenbroich, P, J Merlot & H Schrader. (2022). Dieser Messwert hätte das Umweltamt alarmieren müssen. SpiegelPanorama, 17 August 2022.

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