Success in combating golden algae – an experiment on the Kłodnica River

In the summer of 2024, a team of scientists conducted an experiment involving the use of hydrogen peroxide to limit the bloom of Prymnesium parvum algae in the Kłodnica River in Silesia. The method proved highly promising, allowing researchers to formulate basic guidelines for preventing future toxic algae blooms.

Seasonal and geographical context of the experiment

The bloom of golden algae in 2022 caused an ecological disaster on the Odra River, resulting in 249 tons of dead fish being collected across five provinces within a few weeks. Unsurprisingly, experts have been working for two years to develop methods to combat this lethal haptophyte, which has found particularly favorable conditions for growth in the Gliwice Canal. The Kłodnica River was selected as the site of the experiment because the problematic canal flows into it before continuing on to the Odra.

In early August 2024, large amounts of Prymnesium parvum were detected in the Dzierżno Duże Reservoir, with increasing concentrations also found in the Kłodnica River. The risk of another ecological disaster prompted scientists to attempt the use of perhydrol, a 35% hydrogen peroxide solution commonly used worldwide for wastewater treatment and algae bloom control, including haptophytes. In Poland, the efficacy of H₂O₂ in combating golden algae had already been confirmed in laboratory tests conducted at the University of Warsaw.

How were the tests with perhydrol on the Kłodnica River conducted?

The experiment [1] was made possible through the successful collaboration of the IOŚ-PIB, GDOŚ, and RDOŚ Katowice, as well as RZGW Gliwice, public officials, and local governments. From August 13, perhydrol was introduced into the river over three weeks via an installation mounted below the Pławniowice water dam. Two water sampling points were established upstream, and four sites downstream were used to assess the actual effects of the substance application.

Throughout the experiment, regular measurements were taken to monitor perhydrol concentrations in different sections of the river. Additionally, researchers assessed water temperature, oxygen levels, pH, redox potential, and the presence of chlorides, sulfates, and nitrogen and phosphorus compounds. Analyses also included biological and chemical oxygen demand, as well as other physicochemical and microbiological parameters. The most crucial part of the study involved measuring the abundance of Prymnesium parvum in the Kłodnica.

Results of the experiment on the Kłodnica River

The application of perhydrol at a concentration of 10 mg/l eliminated golden algae with 90% efficiency, while doses of approximately 15 mg/l achieved an efficiency of over 99%. These results demonstrate that hydrogen peroxide is exceptionally effective in combating Prymnesium parvum blooms. To reduce the abundance of the haptophyte below the warning level set by GIOŚ, a dose of 13 mg/l is sufficient—lower than previously expected.

The experiment on the Kłodnica River also showed that using perhydrol does not pose a significant threat to the natural environment. There was no increase in levels of ichthyotoxins harmful to fish, nor did fundamental physicochemical or microbiological water parameters change significantly. The only issue encountered was a temporary rise in H₂O₂ concentration, caused by reduced water flow through a power plant located upstream of the application site. According to the experiment’s authors, applying perhydrol at recommended doses should not impact fish populations. Other algae also appear to be much more resistant to hydrogen peroxide than haptophytes. However, the tests did affect rotifers (small invertebrates that are part of the zooplankton) and submerged macrophytes.

Experts from the Inland Fisheries Institute PIB positively assessed the results of the experiment conducted on the Kłodnica. However, they suggest careful dosing in future applications and ensuring that fish have the ability to migrate to areas with lower concentrations of the compound. Hydrogen peroxide should initially be introduced at low concentrations to drive fish away, with doses gradually increasing to the target levels.

Despite the positive results, the authors of the Kłodnica experiment caution that these findings apply only to the local situation. In different environmental conditions, combating golden algae with hydrogen peroxide may yield varying results.

[1] https://ios.edu.pl/wp-content/uploads/2025/01/raport-eksperymentalne-zastosowanie-nadtlenku-wodoru-do-ograniczenia-zakwitu-prymnesium-parvum-w-rzece-klodnicy-latem-2024-r.pdf

Main photo: gov.p