What's killing the fish? Czech researchers are looking for answers
Rising temperatures and declining oxygen levels are causing more frequent fish die-offs in Czech rivers, prompting new efforts to monitor and protect freshwater ecosystems. Scientists and water authorities are deploying advanced technologies to track water quality and better understand how climate change is reshaping aquatic life.
During hot summer days, one of the most common ways to cool down is by going for a swim. As the Czech Republic is a landlocked country, people rely not only on swimming pools but also on natural bodies of water such as rivers and lakes to escape the heat. While it may not be obvious at first glance, these waters are also suffering the consequences of global warming. Among the organisms affected are fish.
Scientists have been observing a growing number of fish die-offs for several years. The main factor behind this trend is the depletion of oxygen caused by the overgrowth of cyanobacteria, which thrive in warm water during hot weather.
At the end of June last year, around 30 tonnes of fish died in the Morava River's Dyje tributary. This year, the state-owned company Povodí Moravy, which manages the Morava River basin, is trying to prevent a similar disaster. Monitoring probes have been installed along the river to measure water temperature and oxygen levels both at the surface and at greater depths. The data are transmitted directly to the river authority, which assesses whether interventions, such as adjusting the river flow, are necessary. In some sections, the water has also been artificially oxygenated. Thanks to these measures, fish deaths have so far been prevented this year.
Watercourses are now also being monitored on the opposite side of the country, in the Ore Mountains, which lie along the border between the Czech Republic and Germany. The main part of a three-year research project will focus on quantitative monitoring of fish populations in selected streams across the mountain range.
"This project has several phases. In the first phase, we will install temperature sensors along approximately the first half of the stream to monitor water temperature over the long term. The second phase, which is the most important one, will involve visiting each site individually and conducting a detailed survey of both the aquatic environment and the relevant abiotic factors," says Petr Blabolil, the project leader from the Biology Centre of the Czech Academy of Sciences and the University of South Bohemia.
The Ore Mountains have undergone major changes over recent decades due to industrial pollution, landscape restoration, and ongoing climate change. The project therefore also aims to find out what condition the local fish communities are in today and which factors will shape their future development.
During fieldwork, biologists will carefully catch, measure, weigh, and identify fish before releasing them.
"We would like to find some unique, locally adapted populations and assess their status and condition. Then we will focus on other populations and examine whether they are doing well or whether it is necessary to take additional measures to help them thrive better in the future," Petr Blabolil adds.
The overall aim of the project is to improve the protection of the Ore Mountains' native freshwater ecosystems and to establish a shared scientific foundation for their long-term management on both the Czech and Saxon sides of the border.
