Firefighters in Breclav help fishermen in a large-scale cleaning operation last week to wipe out dozens of tonnes of suffocated fish on the Dije River in South Moravian. According to Zdeněk Blavla, chairman of the Moravian Fisheries Association, the Czech news agency reports that it is about one-tenth of the total amount of fish caught so far, or about 9 tonnes.
Fish death is due to a lack of oxygen caused by an excess of cyanobacteria. Cyanobacteria consume oxygen at night and tend to grow during hot weather, when the water level is low and the concentration of phosphorus, the main nutrient required by the bacteria, is higher than normal. According to Petr Chmelař, a spokesman for the Moravian basin, phosphorus usually flows into rivers because water treatment plants do not properly remove phosphorus during the cleaning process.
Dead fish are being transported to a rendering plant for processing. Among the dead fish are carp, zander, catfish and sea bream. Fishermen estimate that the damage caused by dead fish lies in millions of crowns.
https://english.radio.cz/clean-operation-dead-fish-dyje-river-begins-8756755 Purification of dead fish on the Dije River begins