Article by Patryk Strzałkowski, journalist at Gazeta.pl.
105 tons of dead fish—that is the latest, and likely not final, tally of the ecological disaster at the Dzierżno Duże reservoir in Silesia. At the beginning of August, a massive amount of golden algae, a type of algae that was responsible for the mass fish die-off in the Oder River in 2022, was detected there. Anglers first noticed dead fish, and soon after, together with the authorities, they were removing tons of them daily.
The scale of the disaster is significant for a single reservoir, but its scope was smaller than in 2022 when it affected a large section of the Oder River. "The scale of the disaster at the Dzierżno reservoir is completely different from two years ago on the Oder. Back then, 1,650 tons of fish died," Jacek Engel from the Greenmind Foundation and the Save Our Rivers Coalition told us.
The fact that a catastrophic bloom of golden algae—which under certain conditions releases a substance toxic to fish and mussels—occurred is not surprising to experts. They had warned about it in reports and interviews, as we have also repeatedly written about on Gazeta.pl.
Environmental organizations have long been sounding the alarm that the quality of water in Polish rivers is terrible, and for two years, we have been warning that the problem with golden algae would reappear. And it has, and it is not at all certain that this will be the end for this year. If we continue to have high temperatures and low flow in the Oder, it cannot be ruled out that the fish die-off will continue
says Karol Ciężak from the Society for the Earth.
Rivers as Salty as the Sea
Could the disaster at the Dzierżno reservoir have been avoided? According to Engel, it's difficult to give a definitive answer. "The key is to reduce the discharge of saline water into the Oder and its tributaries. We've known for two years that salinity is one of the sources of the problem, as it allows golden algae to thrive. More could have probably been done during this time," he believes. Ciężak also emphasizes that there was time to take actions to limit the discharge of brines and to review permits for discharging saline water. "At the very least, we should limit the discharge of saline water during low flow periods. That's fundamental," he says.
Golden algae (Prymnesium parvum) is an invasive species of algae in Poland that produces prymnesins, which are toxic to fish. It thrives in fairly saline waters, so theoretically, freshwater rivers should not be a good environment for this algae. However, rivers in Poland, including the Oder, are very saline, mainly due to the discharge of brines pumped out from mines.
Salinity can be particularly extreme in rivers and reservoirs in Silesia. For example, in the Gliwice Canal—which connects to the Dzierżno reservoir (itself an artificial post-exploitation reservoir) and later to the Oder—salinity is often much higher than in the Baltic Sea. According to recent measurement data, the water conductivity (an indirect measure of salinity) in the upper Oder near the Czech border is 525 µS/cm, and already in the Opole Voivodeship, it reaches 1920 µS/cm. At the beginning of the Gliwice Canal, it is over 11,000 µS/cm.
This extreme salinity—combined with other pollutants that provide nutrients for algae—allows for algal blooms, which can result in the release of toxins and the death of fish.
The coal mines were given a license to kill by the previous government, and they are still using it. How else can you describe the nearly unrestricted ability to discharge saline waste into the tributaries of the Oder and Vistula? Hundreds of thousands of dead fish in the Dzierżno reservoir is yet another chapter in an ongoing two-year catastrophe - said Katarzyna Bilewska from Greenpeace. In her opinion, the government is only taking short-term measures, and "despite Donald Tusk's promises, Polish rivers are still not protected from the discharge of saline waste from mines."
What About Monitoring?
When the disaster on the Oder occurred, much was said about the lack of adequate monitoring of water quality in the river and its tributaries. Has there been any improvement in this area?
"In terms of monitoring, it's actually worse now," says Jacek Engel, explaining: "The Environmental Protection Inspectorate is legally responsible for environmental monitoring, including water quality. But under the previous government, 250 million PLN was allocated to build a completely alternative surface water monitoring system by the Inland Fisheries Institute. Its concept doesn't make sense because it includes hundreds of stations, but they measure only a few parameters. Meanwhile, we need fewer stations but ones that measure much more."
The new government also criticizes the previous administration's monitoring plans and the state of their implementation—last August, the Ministry of Climate filed a report to the prosecutor's office regarding this matter.
To better coordinate activities related to the river, an Interministerial Team for the Oder was established, and the Dzierżno incident was coordinated by a crisis management team. However, Engel believes that there seems to be some "competition" between the Ministry of Climate (responsible for environmental protection) and the Ministry of Infrastructure (responsible for water management) over who better protects the Oder. The Ministry of Climate reported on its experiment to combat golden algae, while the Ministry of Infrastructure touted the "success" of a completely different method (using a silicon-based agent).
"It looks like they are competing with each other, but the Oder should be the priority, not political ambitions. Restoring oversight of water management to the Ministry of the Environment would improve the situation. It's a simple measure that only requires a decree from the Prime Minister," says Engel.
A Band-Aid on the Wound
The experiment overseen by the Ministry of Climate involves neutralizing golden algae with perhydrol (hydrogen peroxide). The agent is supposed to be effective in fighting algae while being safe for fish. The Ministry of Climate declared it a success, as the experiment in the Kłodnica River (which connects to the Dzierżno reservoir and flows alongside the Gliwice Canal) showed that after applying the agent, the amount of golden algae decreased by 95-99 percent.
However, environmental organizations have doubts—mainly about the scale. "I view the government's actions surrounding the 'experiment' with perhydrol as unserious. Other countries' experiences show that it can combat Prymnesium parvum. But in all the publications I've seen on the subject, it's about small bodies of water, not entire rivers," says Jacek Engel from the Greenmind Foundation.
"Experiments like those with hydrogen peroxide might save something in extreme situations, but I can't imagine dumping it into the entire Gliwice Canal," says Karol Ciężak. Together with his research team, he is working on an independent monitoring system to track the effects of hydrogen peroxide on small aquatic organisms.
It must be acknowledged that the ministry itself also emphasizes that the use of hydrogen peroxide is a "crisis measure," not a long-term solution to the problem. "Work is currently underway on creating a plan to reduce water salinity, one of the main causes of the golden algae bloom in the Oder," the ministry reports.
NGOs also believe that addressing salinity and improving water quality is crucial to combating golden algae. And there is no time to lose because the Oder, the Vistula (which is also saline in some sections), and reservoirs like Dzierżno could become hotspots for algal blooms at any moment.
The amendment to the Oder Special Act has been postponed, now scheduled for the fall. Yet, the government received a proposal from the Frank Bold Foundation a long time ago. Additionally, we hear that the fee for saline discharge will not be changed. Currently, it is a paltry 5 groszy per kilogram
says Engel. He believes that it is crucial for mines to start paying for the environmental damage caused by discharging saline water into rivers. "The fee should be high enough to make it more cost-effective to build desalination systems or reinject saline water into the ground," he emphasizes.
Another solution he mentions is the creation and use of retention reservoirs. Saline water from the mines could be stored there during periods of high temperatures and low flow, when the risk of algal blooms is high. "It's much cheaper than desalination systems. The bill prepared under the PiS government included incentives for retaining saline water, but it has only been in effect for five days—yet the low water period on the Oder in 2022 lasted 80 days, so it's laughably short," he says.
