In recent days, fishermen, in cooperation with firefighters, have been completing the catch of dead fish on the Dyje River in the Břeclav region. According to the fishermen, the amount of fish was huge, but the exact number cannot be determined, as some of the fish were decomposed due to the weather. According to fishermen and the Morava River Basin, similar disasters may recur.

In the first hours after the deaths, local fishermen pointed at the water managers, saying their bad work was behind the deaths below the Nové Mlýny reservoir. After emotions cool down, the fishermen’s leadership and water managers discuss a joint approach.

“According to experts, there are several factors that cause such incidents. The main one is the overabundance of nutrients in the waterways, especially phosphorus. Our common goal should therefore be to improve the quality of wastewater treatment and tighten the limits for discharging waste substances into water streams,” Jiří Ryšánek, chairman of the Moravian Fishermen’s Association, wrote.

Not enough oxygen

According to Petr Chmelař, spokesman for the river basin district, it is not only the rivers of the South Moravia region that have been struggling with water shortages and, therefore, low flows for a long time. A recurrence of fish kills cannot be ruled out.

Water managers are trying to help the river and are releasing more water from Nové Mlýny than is flowing into the reservoir.

“In the ten days since the first mortality, we have released 12 percent of the reservoir in this way, which cannot be maintained indefinitely at a similar flow. Moreover, we have to keep in mind the fish in the reservoir,” Chmelař pointed out.

According to measurements, the amount of oxygen in the Dyje is still low, and water managers have outlined that the disaster would probably have happened if the fish had not died ten days ago.

“Oxygen is disappearing due to temperature and water bloom, but it is impossible to say if and when the situation will be good or bad because even experts disagree on what exactly the cyanobacteria are reacting to. We did have a relatively rainy weekend, but it didn’t help significantly,” Chmelař said.

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