Toxic golden algae bloom in Gliwice Canal kills over 150 kg of fish in single day

Toxic algae bloom in Gliwice Canal

Wody Polskie in Gliwice confirmed the presence of Prymnesium parvum, commonly known as golden algae, in the waters of the Gliwice Canal in Silesia. The microorganism's bloom can have toxic effects on aquatic organisms. Since the beginning of August, the algae's population has been increasing rapidly in the canal's waters, according to monitoring by environmental services. Services had been reporting increased concentrations of golden algae in the Gliwice Canal for several days before the fish deaths escalated.

Rising fish death toll

Workers removed approximately 12 kg of dead fish from section VI of the Gliwice Canal on Saturday morning, 15 August, followed by another 22 kg in the afternoon, bringing Saturday's total to 34 kg. On Sunday morning, 16 August, crews recovered approximately 157 kg of dead fish from the same section, nearly five times the previous day's total. The dead fish included bream, carp, and perch. No dead fish were found in other sections of the waterway. Removal operations are expected to continue.

Emergency measures

Wody Polskie implemented recommendations from the Interministerial Team for the Odra River to limit the risk of golden algae bloom. Water flow downstream in sections V and VI of the Gliwice Canal was completely halted, and lock operations at the Łabędy and Dzierżno locks were suspended until further notice. Patrols are being conducted from both water and land along the entire length of the Gliwice Canal, with particular focus on sections IV, V, and VI, as well as the Dzierżno Duże reservoir. Wody Polskie secured equipment for use by other services and is transmitting information about irregularities to institutions including the Provincial Inspectorate of Environmental Protection in Katowice, Veterinary Inspection in Katowice, Polish Angling Association in Katowice, State Fire Service, and crisis management services at voivode, county, and municipal levels. The event was also reported to the Provincial Crisis Management Centre of the Silesian Voivodeship Office.

The priority is to limit the risk of further spread of golden algae and the rapid removal of dead fish.

Further actions will depend on the development of the situation, according to the communication.

Historical context and countermeasures

Scientists identified Prymnesium parvum as the direct cause of the ecological disaster on the Odra River in 2022, when mass deaths of fish, mussels, snails, and other gill-breathing organisms occurred. The same organism caused mass deaths in the Dzierżno Duże reservoir in 2024. In March and April 2022, over 8 tons of dead fish were removed from the Gliwice Canal, with smaller-scale recurrences in early spring 2023 and 2024. Dead fish were also removed from the Łabędy lock in March of last year.

Silesian voivode Marek Wójcik announced that services are prepared to use hydrogen peroxide (H2O2) if necessary, which effectively combats golden algae. In 2024, an experiment on the Kłodnica River using hydrogen peroxide to neutralize golden algae reduced the algae's population by over 90 percent, according to a report by the Institute of Environmental Protection, a national research institute. The development of golden algae in the Gliwice Canal is favored by a combination of factors including water stagnation, heating during heat waves, and high salinity levels. The next meeting of the Interministerial Team for the Odra is scheduled for Tuesday, 18 August, when decisions on further steps may be taken.