Tragedy – this is how one can sum up in one word what is happening on Lake Dzierżno Duże. In the reservoir, which is connected to the Oder via the Gliwice Canal, an ecological disaster has been going on for two weeks. And the situation is getting worse day by day. Only 15 August 16 tons of dead fish were pulled from the water.
Dead fish began to appear in the lake in early August. A very large amount of golden algae was also detected – an algae that releases a substance toxic to fish and crustaceans. The algae bloom in reservoirs connected to the Oder was the cause of a major ecological disaster on the river in the summer of 2022. Since then, experts have warned that without combating the causes of the problem (pollution, salty water from mines that allow the algae to grow), the disaster will repeat itself. This dark scenario is now being realized not on the river itself, but on Dzierżno Duży.
When we tried to contact the local fishing club on Friday morning, no one had time to talk – everyone who could have appeared was on the water and engaged in removing dead fish. The task is gigantic, because the number of animals is growing. On August 13, 2.5 tons were pulled out, a day later 4.5 tons, and on Thursday – as many as 16 tons. In total, from August 3 to Thursday (midday), 55 tons of dead fish were taken from the lake, and thousands of kilograms more removed from fragments of the Gliwice Canal.
The action involves anglers, employees of Wody Polskie, firefighters and WOT soldiers. The largest number of dead animals is recovered from the beach on the side of Rzeczyce and in the so-called ponds.
Fighting the stench and time
In the reports of the local branch of the Polish Angling Association we read about the extremely hard work involved in removing dead fish – and also about the fact that in the two years since the disaster on the Odra, nothing has been done to prevent a repeat, this time on the lake.
This is how the local portal “Today in Gliwice” describes the situation:
The unimaginable stench, dozens of bustling people, the howling of generators, soldiers, firefighters, bags arranged along the shoreline like a flood embankment… They are not filled with sand. They contain TENS OF THOUSANDS OF KILOGRAMS of dead fish. They are dead because, as the fishermen say, nothing has been done for two years. “The lake is practically dead,” they add.
The fishing club is also trying to find a haven for the fish that are still alive. It is a race against time, because the number of dead fish is growing. It is also not known how many dead fish are lying on the bottom – only those on the surface are being pulled out.
Experimental fight against golden algae
At the moment, the only good news is that there are no dead fish in the remaining sections of the Gliwice Canal, the Kędzierzyn Canal or other reservoirs in the region. Therefore, in addition to the removal of fish by the services, the authorities' actions are focused on limiting the scope of the disaster.
Water from the lake, and with it the cause of fish deaths, could get through the Gliwice Canal to the Oder. Then even more animals would be at risk. Special barriers were set up earlier to prevent this. from bags filled with straw. So-called “biostabilizers” are intended to prevent the growth and spread of golden algae.
On Wednesday, an experimental dosing of hydrogen peroxide (H2O2) into the waters of the Kłodnica River, which connects with the Gliwice Canal above the lake, began. The aim is to check whether the substance is effective in reducing the number of golden algae. Hydrogen peroxide is used to combat cyanobacteria. According to the Ministry of Climate and Environment, “it decomposes in water into oxygen and water, leaving no by-products”. The experiment is supervised by, among others, experts from the Institute of Environmental Protection – State Research Institute, and the execution is assisted by soldiers from the 5th Chemical Regiment in Tarnowskie Góry. Deputy Minister of Climate Urszula Zielińska participated in the crisis team meetings.
If the experiment is successful, it will be possible to use hydrogen peroxide to stop golden algae blooms in the future. However, the ministry itself points out that “this is not a systemic solution” and the Inter-ministerial Team for the Odra River is working to ensure “the safety of the Odra ecosystem”.
Long-term actions are to be based on limiting the salinity of water in the Oder and its basin. High salinity – which is primarily related to the discharge of saline water from mines – is one of the main causes of the problem, because golden algae grows in saline water. Government It also wants to introduce changes to the special act on the Odra, which was prepared by the previous government in response to the disaster. The main direction is to be the renaturation of the river.