In the summer of 2022, an environmental disaster occurred in the Oder River: an estimated 1,000 tons of fish, mussels, and snails died. This began in the Polish part of the Oder and continued downstream into Germany. The cause was a toxic brackish algae called Prymnesium parvum.
The Oder has its source in the Czech Republic and flows into the Baltic Sea in the Szczecin Lagoon. It forms the border between Germany and Poland.
The Oder is 840.9 km long. Due to regulations and construction, its length has shrunk by more than 20%. Its drainage basin covers 124,049 km², with 86.4% in Poland, 5.9% in the Czech Republic, and 7.7% in Germany.
The fish die-off in the Oder in August 2022 brought to the fore the challenges facing environmentalists and politicians despite years ofprogress in the field of water protection. . Hot and dry summers resulting from climate change can cause such events in the Oder and other waters. Factors include changing environmental conditions and human activities (e.g., industrial discharges or extensive water regulation).
In the Oder, multiple stressors – high salinity, sunlight, high water temperatures, and low water levels – overwhelmed the ecosystem’s natural resilience, allowing the brackish algae Prymnesium parvum to thrive.
Algae blooms in water bodies are caused by many factors, including nutrient inputs like nitrogen and phosphorus from agriculture and sewage treatment plants, as well as light and warm temperatures. The fish die-off in the summer of 2022 was caused by Prymnesium parvum and its toxins, which could multiply rapidly under extreme environmental conditions.
Prymnesium parvum is a single-celled organism that usually occurs in brackish and marine waters but can also be found in inland waters. It is found worldwide, including in Europe, China, Australia, the USA, and North Africa.
The algae produces prymnesins (toxins) that can destroy the gill tissue of fish and shellfish.
In water bodies, various salts can accumulate depending on discharges, natural background, or inflows. Salts enter waters through sewage treatment plants, road surfaces, and especially mining. In brown coal mining, saline brine can be a by-product. In the Oder, rock salt (sodium chloride) from mining is significant. Therefore, the salinity there is mainly represented by chloride ions. Algae blooms of P. parvum can occur at chloride concentrations from >300 to >30,000 mg/l, with blooms forming at 350 mg/l.
The Prymnesium algae are widespread and become resilient over time. There are no effective measures to reduce or remove it from flowing waters. Significantly reducing salinity would minimize algae growth. Growth-promoting factors like high nutrient and salinity concentrations must also be avoided.
An environmental disaster in the Oder is still possible. Initial regional fish die-offs were reported in the Oder in Poland and Germany in June. Rising algae concentrations triggered the first warning levels in Poland and Brandenburg in June 2024. The salt levels in the Oder remain consistently high in 2024. Compared to the fish die-off in August 2022, water temperatures are currently lower, and water volume and levels are significantly higher. This is good news, as the algae prefer standing and slow-flowing waters. For this reason, the algae have also been detected in some side waters and stagnant water bodies.
In May 2024, the bilateral expert group on the Oder, established after the 2022 fish die-off, was reactivated to facilitate an exchange of information between Poland and Germany. The German co-chair is the Federal Environment Agency (UBA). In this group, Polish and German experts share updates on the Oder, discuss measures for crisis management, and exchange data on monitoring, facts, and new scientific findings. There is open, transparent, and proactive communication between Polish and German authorities.
Crises like the 2022 fish die-off in the Oder are hard to predict because many environmental factors influence the water, and it's unclear when the system's limits is exceeded. However, everyone involved has learned from the disasterand worked together to address it. Initial results from a research project funded by the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety, and Consumer Protection (BMUV) are available. Warning systems have been developed in Brandenburg and Poland. The warning and alarm plan of the International Commission for the Protection of the Oder (ICPDO) was adjusted to detect fish die-offs.
Ecological disasters like in the Oder in 2022 require coordinated action by all involved: early detection and assessment of events, pooling activities and knowledge in a crisis, and quick political decisions. In such crises, ecological damage must be recorded, and measures to strengthen the resilience of waters and ensure sustainable protection must be derived.
Currently, data on water monitoring are provided on various internet platforms of the states and the federal government. Integrating these online measurement data and linking them with forecasting tools could improve monitoring and crisis detection. New methods such as remote sensing to detect algae blooms via satellite data or genetic studies (eDNA) to capture aquatic communities in much more detail can also help.
For early detection, continuous, timely evaluation of online data and close coordination between states and federal authorities are important
In case of accidents or fish die-offs, there are cross-border warning and alarm plans for major rivers, including the Oder. For cases like a mass fish die-off, a coordinated process chain from warning to communication is crucial; crisis scenarios should be prepared to take immediate action in emergencies, such as significantly increased pollutant concentrations with severe ecological consequences. It also helps to know which authority or institution has the right expertise to investigate specific issues nationwide. A responsive network is a prerequisite for this.
Documenting a crisis is important for clarification and later review. After the Oder fish die-off, a status report by the German expert group was created and made available to the public. The Federal Institute of Hydrology (BfG) also reviewed the environmental disaster and the support it provided on behalf of the BMUV in a report.
Sampling continues after the fish die-off. Coordinated plans for sampling and logistics are necessary. Long-term sample storage is possible through the Federal Environmental Specimen Bank. Follow-up monitoring should be coordinated, and data should be secured and evaluated long-term. The Federal Ministry for the Environment funded a special three-year investigation program for the Oder to assess ecological damage and monitor the ecosystem's recovery.
The Federal Environment Agency (UBA) coordinated the investigation of the 2022 fish die-off in the Oder and led a German-Polish expert group with a Polish colleague. It continues to communicate with Polish authorities, German states, and a network of science and research. The UBA continues these tasks in 2024.
The UBA's wide range of topics, including water assessment, monitoring, pollutants from industry and municipalities, mining, algae, and their toxins, and established cooperation with state and other federal authorities, provides a solid basis for evaluation, clarification, and recommendations in coordination with all parties involved. This scientific expertise supports the Federal Ministry for the Environment and promotes communication and cooperation with the states through various committees.
The UBA analyses existing data on water quality nationwide and conducts risk assessments for saline waters. It researches new techniques for determining aquatic communities to develop more efficient methods for water monitoring. Based on this, the UBA makes action recommendations, identifies knowledge gaps, and designs research approaches for future water monitoring. The UBA also informs the public and answers questions from the media and citizens.
The Oder fish die-off in 2022 was caused by several factors: high salt concentration, high nutrient levels, high water temperature, and low water level. Recommendations include:
Overall, more efforts must be made to make waters more resilient to disasters and climate change, through natural and technical adaptations. This requires regional planning and measures such as reactivating floodplains, improving water continuity, removing bank and bed reinforcements, and reducing nutrient and pollutant inputs.
