Polish authorities have found toxic golden algae in the River Oder, which runs along the country's German border.
The golden algae had been washed into the river from the Gliwice Canal, the crisis unit of the Polish Ministry of Climate and Environment announced on Friday evening.
The highest risk level had been imposed for the section of the river near the town of Lany, south-east of Wroclaw.
Many dead fish have been discovered in the Gliwice Canal, which branches off from the Oder, since last week. According to experts, "the ability of the golden algae to thrive in the dynamic current of the Oder is limited compared to the conditions in the stagnant waters of the canal," a ministry press release continues.
However, the low water level of the Oder observed since the beginning of May is an additional factor that increases the risk. The Gliwice Canal, which was opened in 1939, is 41 kilometres long and connects the Upper Silesian city of Gliwice with the Oder.
In the summer of 2022, a mass fish kill occurred in the Oder. Experts in Germany and Poland came to the conclusion that the toxic effect of a bloom of the poisonous golden algae Prymnesium parvum had most likely caused the death of the fish.
The crisis team now wants to ensure that as little as possible of the golden algae, which has proliferated in the Gliwice Canal, gets into the Oder.
To this end, the Polish water authority has been instructed to minimise the sluice openings on the canal and to control the water flows accordingly. In addition, the state of the water and the terrain along the river are regularly inspected.