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Endless quantities of dead fish in the Oder hit the media headlines in July and August 2022, making it one of the largest ecological disasters in Europe in recent memory. Two questions followed: what caused the fish to die? And how can such catastrophes be prevented from happening again?

These questions are exactly what a technical report by the European Commission’s Joint Research Centre tries to answer. The report, supported by the EEA experts and EEA data, identifies the likely causes and proposes recommendations to help prevent such incidents.

According to the scientific evidence in the report, the deaths of around 360 tonnes of fish were caused by a substantial toxic algal bloom identified as 'Prymnesium parvum'. A key factor that enabled the proliferation of this brackish water species is most likely the high salinity of the Oder River during that time, resulting from discharges of industrial wastewater with a high salt content, for example, from activities such as mining.

Other contributing factors mentioned in the report include the drought and the resulting low water levels reducing dilution and flow. Elevated nutrient concentrations, especially phosphorus and nitrogen, are also a key component causing such blooms.

This invasive algal species is present and continues to spread in many European rivers. Given this, not only the Oder catchment but also other susceptible river basins must prioritise management strategies to prevent future occurrence of events of this nature, the report underlines.

The report highlights key recommendations to prevent future ecological disasters in EU rivers:

  • Improve knowledge and monitoring;
  • Undertake research to improve knowledge and help prevent algae growth and salinisation;
  • Improve proactive communication to stakeholders, public and countries downstream;
  • Improve response and risk management (anticipate responses and prepare resources);
  • Review and verify existing permits and increase enforcement. Introduce provisions for allowable pollutant loads to be adapted to the water levels in the recipient waters;
  • List all industrial discharges in a complete and up to date public inventory of emissions (European Industrial Emissions Portal (europa.eu));
  • Further investigate the source of the incident (while a multifactorial event, sources of discharges of saline material should be identified and checked against permits, compare to long term salinity levels);
  • Improve environmental management (hydromorphological changes, salinity/nutrient thresholds);
  • Start restoration (inventory of damage, develop plan for restoration of the river).

EU legislation to further reduce pollution on the way

In the context of its zero pollution action plan, the European Union has been taking concrete steps to reduce pollution and its impact on human health and the environment. Emissions to water from large industrial installations are currently regulated by the Industrial Emissions Directive.  The European Commission has proposed to strengthen to further reduce emissions to water and air.

The European Commission has also put forward a proposal to strengthen the law on treatment of wastewater. When adopted, this will further contribute to preventing nutrient pollution and resulting algae blooms.

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