Toxic algae kills over 4 tonnes of fish in Poland's Gliwice Canal

August 25, 2026 at 12:15 AM2 min

This digest was compiled by AI from multiple sources — links to the originals are below.

More than 4 tonnes of dead fish have been collected from Poland's Gliwice Canal after a bloom of toxic golden algae. Authorities closed two canal locks to stop the algae spreading toward the Oder River. The same species caused a mass fish die-off in the Oder in 2022.

Key Facts

More than 4 tonnes of dead fish have been collected from the Gliwice Canal.
On August 14, golden algae density exceeded 529 million cells per litre in one section of the canal.
Authorities stopped operation of two canal locks to prevent the algae from spreading toward the Oder River.
The same algae species, Prymnesium parvum, caused a mass die-off of hundreds of tonnes of fish in the Oder River in 2022.

Algae Bloom

The source of the fish deaths was identified as Prymnesium parvum, a microscopic golden algae. On August 14, measurements in one section of the canal showed golden algae density above 529 million cells per litre. A few days earlier, the same location had about 270 million cells per litre. The rapid rise led authorities to declare the highest threat level. Golden algae multiply quickly in warm, low-water conditions with high salinity and excess nutrients.

Containment Measures

Authorities stopped operation of two canal locks to limit water movement and prevent the algae from spreading toward the Oder River. If the situation worsens, controlled application of hydrogen peroxide is among the options. This method was previously used in the region to break down golden algae cells. Officials say the intervention will be applied only if deemed necessary. Regular water measurements and land patrols continue in the area.

Oder River Risk

The same algae caused a major environmental disaster in the Oder River in 2022, killing hundreds of tonnes of fish and other aquatic life. A similar crisis occurred in the Gliwice Canal and nearby waters in 2024. Authorities are collecting dead fish and taking regular samples to monitor algae density. The main concern is that the toxic bloom could spread from the canal into a wider section of the Oder River.