Problem
Problem
The Oder River, Poland’s second-longest, flows through the heart of Central Europe, starting in the Czech Republic's Oder Mountains and making its way to the Polish border. It creates a natural boundary between Poland and Germany before reaching the Baltic Sea near the Polish city of Szczecin [1], [2].
The Oder is more than just a waterway – its waters have shaped the landscape and lives of the people it touches, carrying centuries of history on its currents. Its navigable waters are vital to Poland’s economy, supporting transport and trade. But beyond its economic importance, the Oder is home to a rich variety of ecosystems and species, making it a vibrant and diverse natural haven.
Along its shores, we find well-preserved forests, species-rich floodplains and meadows, along with serene backwaters typical of river valleys. Many of the plants and animals that call this region home are listed on regional and national Red Lists of endangered species. The Oder also serves as one of Central Europe’s most important ecological corridors, enabling species to migrate and linking distant habitats. Many areas along its shores are safeguarded under European-level protection [1].
In the summer of 2022, disaster strikes. On August 9th, a wave of dead fish, clams, crayfish and other wildlife washes ashore along the Oder River. Towns along the river warn their residents to avoid contact with the water and not to consume its fish.
The situation escalates rapidly. Within two weeks, hundreds of tons of dead fish are found in the water or washed up on the banks [3]. Confusion and fear spread among the riverside communities as misinformation floods the media.
The community is left searching for answers for weeks, leading to many theories circulating in the media. Some suggest toxic waste from nearby industrial plants, while others point to heavy metal poisoning, pesticides, or even the presence of cyanobacteria or algae. Additionally, many highlight the exceptionally high summer temperatures combined with low water levels in the river as potential factors [4]. Yet, the full picture remains uncertain.
Finally, data from the monitoring station in Frankfurt/Oder, Germany, present a surprising picture: elevated pH and oxygen levels, along with significant fluctuations throughout the day. Such dynamics can only be attributed to one thing – photosynthesis. This leads to the ultimate cause of the disaster: a massive algal bloom.
Researchers analyze water samples, and what they discover is striking for European freshwater environments – a large-scale presence of Prymnesium parvum, known as the “golden algae” [3].
Finally, the cause of the disaster is identified, but this revelation brings a host of new questions along with the answers. What exactly is Prymnesium parvum, and how did it find its way into the waters of the Oder? How could it lead to the death of such a vast number of fish in such a short time? And perhaps most importantly, what steps can we take to address this issue?
Prymnesium parvum is a single-celled microalgae that measures about 5 to 10 micrometers in length. It moves through water using two flagella and can attach itself to prey organisms and surfaces with a structure called a haptonema. This mixotrophic organism can produce its own food through photosynthesis, but it also acts as a predator, feeding heterotrophically on other organisms.
Microscopic image of a water sample containing Prymnesium parvum and schematic diagram of the microalgae.
Under certain conditions, Prymnesium produces toxins known as prymnesins. These toxins can destroy the gills of aquatic organisms, entering their bloodstream and internal organs, ultimately leading to their death, with Prymnesium benefiting from the released nutrients.
Prymnesium is primarily found in brackish waters worldwide, as well as in oceans, though at lower concentrations. While the algae was present in Europe before the 2022 disaster, toxic blooms were typically seen in regions with naturally high salt content. This makes the Oder River disaster particularly surprising and concerning, as it represents one of only two known mass developments of Prymnesium parvum in a natural freshwater body, the other being in an industrially polluted river in the northeastern United States [4].
The ecological disaster affecting the Oder is now recognized as a compound event. A complex combination of elevated salt concentrations, nutrient pollution, extreme water temperatures, and low river discharge during a heatwave are believed to have created the perfect conditions for the mass proliferation of Prymnesium parvum in the river [5].
While we have gained a better understanding of the causes and sequence of events that led to the disaster, the biology of its main culprit still remains somewhat shrouded in mystery. Moreover, recent studies indicate that global warming, water use intensification, and chronic ecosystem pollution could increase the likelihood and severity of such compound ecological events in the future [5].
Currently, dead fish no longer accumulate along the Oder’s shores as they did in the summer of 2022. However, this does not mean the problem is resolved – since then, Prymnesium has become established in the Oder system and high concentrations are still being reported [6], [7]. The only difference from 2022 is that signs warning of the algae’s presence in the Oder's waters are largely ignored by those enjoying the river’s offerings, as people continue to swim and fish despite official recommendations.
Sign Translation: Prymnesium parvum, known as "golden algae," has been detected in the water reservoir. Do not use the water to avoid spreading the algae to other bodies of water. REMEMBER: If you notice a change in water color, foam, or dead fish, report it to the Voivodeship Inspectorate for Environmental Protection in Wrocław. IMPORTANT: Objects that have come into contact with the reservoir's water must be thoroughly disinfected before reuse.
People fishing in the Czernica reservoir, which is directly connected to the main channel of the Oder River. This photo was taken on the same day as the above picture of the sign warning against fishing in the water due to the presence of Prymnesium parvum.
A significant challenge still remains: the analysis of water samples containing Prymnesium parvum relies on time-consuming microscopic identification by researchers, requiring access to laboratory equipment and trained personnel.
As a team of young researchers passionate about nature and its conservation, we couldn’t just stand by while this problem persisted – we had to take action. We envision a world where everyone, regardless of their scientific background, can quickly and effectively screen water bodies for the presence of Prymnesium parvum, allowing them to safely enjoy all that the Oder River has to offer. We aim to preserve the Oder’s precious aquatic ecosystems in their natural state.
[1] “The Oder,” SaveOder. [Online]. Available: https://saveoder.org/en/the-oder/
[2] “Oder River,” Britannica. [Online]. Available: https://www.britannica.com/place/Oder-River
[3] “The environmental disaster in the Oder River in summer 2022,” ODER~SO. [Online]. Available: https://www.oder-so.info/en/environmental-disaster-oder-river-summer-2022
[4] “Zbrodnia na Odrze, to zbrodnia na nas wszystkich,” WWF. [Online]. Available: https://www.wwf.pl/zbrodnia-na-odrze-zbrodnia-na-nas-wszystkich
[5] J. Köhler *et al.*, “Unpredicted ecosystem response to compound human impacts in a European river,” *Sci Rep*, vol. 14, no. 1, p. 16445, Jul. 2024, doi: 10.1038/s41598-024-66943-9.
[6] A. Tittmann, “State of knowledge on the toxic alga Prymnesium parvum in the Oder River,” *FACT SHEET*.
[7] “Śnięcia ryb spowodowane toksycznymi zakwitami „złotej algi”,” Serwis Rzeczypospolitej Polskiej. [Online]. Available: https://www.gov.pl/web/odra/sniecia-ryb-spowodowane-toksycznymi-zakwitami-zlotej-algi
