Odra

According to scientists, the massive bloom of invasive microalgae was caused by overlapping factors: changes in water parameters, including increased salinity caused by the hydrological drought, the hot weather raising the water temperature o 27°C and significantly more sunshine than in previous years, which accelerates algal growth. These conclusions are based on more than 36,000 tests.

However, the expert team's report does not conclude the investigation into the causes of the massive fish die-off in the Oder River. At the press conference summarising, the team announced further action. What are they?

Andrzej Szweda-Lewandowski: Activities have not ended and are being executed multi-directionally. The teams that have worked within the framework of the expert group the Minister of Climate and Environment set up are still directionally analysing the material and performing further research work. For example, a laboratory at the University of Gdańsk continues genetic studies of the ‘golden algae’ that have appeared in the Oder River. The expected outcome of this work will be the developed complete genetic sequence of this organism. Meanwhile, the Regional Directorate for Environmental Protection in Wrocław keeps conducting proceedings for environmental damage. As part of this procedure, the percentage of population loss of the protected species in the river, among other things, will be determined. An ecosystem restoration plan will be proposed in cooperation with the Inland Fisheries Institute - National Research Institute, which has undertaken work on rebuilding the biodiversity of the Oder, as well as creating a gene bank of Oder fish.

Since we are talking about the recovery of the Oder fish population, do we know today which species have suffered?

AS-L: Estimation is ongoing; several teams from the Institute of Inland Fisheries Institute are currently working on an inventory of the species whose populations have been affected by the Oder incident. It is known that these included large predators, including catfish and pikeperch. The Inland Fisheries Institute - National Research Institute teams are precisely inventorying these species. At the same time, the possibility of creating refugia – places where fish could take refuge in the future, should a similar threat arise. It is important to remember that population recovery will make sense if fish are provided with the right conditions for life and survival.

While we are talking about the salinity of the Oder River, where did it come from?

AS-L: Based on the findings presented in the report, it was concluded that the environmental conditions in the Oder River in July and August 2022, combined with saline water discharges, increased the conductivity and concentration of chloride ions, sulphate and sodium ions. An analysis of the documentation is ongoing, but the findings to date do not indicate that there were any above-normal discharges. Unfortunately, during this period, there was a high temperature, low water levels and slow water flow, and large amounts of sunshine up to 30% higher than in previous years. This combination of factors created optimal conditions for the development and blooms of ‘golden algae.’

Has the ‘golden algae’ toxic effect caused life in the Oder River to completely die out? Will it be possible to restore the fish population, and when?

A S-L: Contrary to popular belief, the Oder is not dead, but the loss of ecosystems is significant. By the end of 2022, a report will be produced on losses among specific species. Restocking will be possible in spring at the earliest when the fish will have food, living and breeding conditions. Fish and other aquatic organisms, especially molluscs, have also been affected in the Oder River. These organisms often live in direct relationships with each other, provide food or even enable individual species to reproduce. They cannot survive one without the other. This is why it is so significant when and with which species the Oder River is restocked. This process should be handled by teams of specialists, including ichthyologists and hydrobiologists. Furthermore, the Oder River should be stocked with species that are native to the Oder, as other species may not survive in the river or may disturb this specific ecosystem.

Could the threat return?

A S-L: A renewed bloom of 'golden algae' in the Oder cannot be ruled out. And here, we are touching on a fundamental issue - the salinity of the Oder River has created conditions suitable for life. However, the experts are still determining whether this factor was behind the massive bloom of this algae and the release of fish-killing toxins. Scientists worldwide can only determine that the algae bloom en masse and release toxins under certain conditions. However, no precise indicators determine that a bloom or release of ichthyotoxins will occur, as one does not necessarily accompany the other. It should also be remembered that 'golden algae' have a wide tolerance to salinity conditions. Therefore, further detailed research is required.

How can similar incidents be prevented in the future?

A S-L: A team set up by the Minister of Climate and Environment in a report on the situation on the Oder River identified specific actions and gave its recommendations. Among the recommended activities is the introduction of integrated water quality monitoring combined with control of hydrological and meteorological conditions. Also advisable is verifying water permits regarding the amount of pollutants that enter rivers, eliminating illegal sewage discharges and exploring the possibility of creating refugia for fish. The report includes a chapter on methods for neutralising 'golden algae' practised worldwide. The solutions presented in the professional literature are currently being analysed in depth. Mainly whether solutions that are proven to work in spots, e.g. in the case of fish ponds in the USA, can be applied to flowing waters in a large river.

Interview: The editorial team at gov.pl/odra