Experts are still trying to determine the cause of death of thousands of fish last week in the Oder River that borders Germany and Poland, this time in the vicinity of the eastern city of Frankfurt (Oder).
The reports came just two weeks after Polish anglers reported removing tons of dead fish from the Oder near the town of Olawa, about 300 kilometers (186 miles) upstream from the more recent fish die-off.
At the time of the reports in Poland, water authorities based in the nearby Polish city of Wroclaw detected a toxic substance in two locations on the Oder that is likely the solvent mesitylene, which is known to have a harmful effect on fish. However, subsequent tests have shown no trace of the substance.
Mercury was also identified as a potential culprit for the more recent die-off. But Polish Environment Minister Anna Moskwa said on Sunday that “completed fish tests for mercury and heavy metals” proved to be negative. Lab tests did show high levels of salinity in the water.
Local authorities have warned residents, along with their pets and livestock, not to touch the river water.
Thousands of dead fish are being collected on the River Oder
Still no proof of poison
While German and Polish authorities believe contamination is the cause of the die-off, political leaders who met on Sunday said water tests gave no definitive proof of high toxicity in the river.
“As of today, none of these tests have confirmed the presence of toxic substances,” Anna Moskwa said after meeting with German Environment Minister Steffi Lemke on Sunday in Szczecin, a city in north-west Poland.
A joint taskforce looking into the cause of the mass fish die-off was also announced at the meeting.
Tests for pesticides and around 300 other substances are also being conducted, the Polish environment minister said.
“We still do not exclude a variant of the toxic substances,” she added. “We are checking entities which run business and industrial activity along the river.”
Meanwhile, no fish carcasses have yet been sighted downstream in the state of Mecklenburg-Vorpommern on the German Baltic coast, officials said.
This follows reports that oil booms will be placed in the Szczecin Lagoon, fed from the Oder, to prevent the dead fish from entering the Baltic Sea.
The River Oder runs though the Czech Republic, Poland and Germany
Heat and drought could be factors
Christian Wolter, researcher at the department of fish biology, fisheries and aquaculture at the Leibniz Institute of Freshwater Ecology and Inland Fisheries, said the problems on the Oder may run deeper.
Fish in the river are struggling, he said, due to lower oxygen levels caused by historically low water levels (a trend since 2018) and high water temperatures of around 25 degrees Celsius (77 Fahrenheit).
“When fish are stressed, respiration goes up,” he said, meaning aquatic life needs more oxygen.
This situation has been exacerbated by ongoing discharges of wastewater into the Oder.
“This is legal and usually wouldn’t matter,” Wolter explained. “But with low water levels you get a higher concentration of [oxygen consuming] salt and organic material.”
Added to the mix is work on the Polish side of the Oder building groins — rigid structures created with rock, soil and gravel to prevent erosion. This has increased sediment, which also reduces oxygen levels in already shallow water, Wolter said.
This contradicts reports from water authorities that higher oxygen levels have been detected in the river, which could be linked to the concentration of mesitylene. Yet there are no measurable high toxic levels to back this claim, according to Wolter, adding that water oxygen levels always vary throughout the day.
The fisheries researcher believes it is less likely that mesitylene contamination killed the fish found this week downstream from Olawa since it already would have dissipated.
“If it was released by an accident at the end of July, it should have passed Frankfurt much earlier,” he said of the toxic solvent.
Meanwhile, local anglers told Wolter that fish die-offs were observed further upstream from Olawa as early as March. This suggests a deeper and more widespread problem than a single contamination event in late July.
Wolter also noted that floodplains in the area have been overly drained in recent decades, causing much drier and stressed river systems.
Polish Greens decry lack of action
Lawmaker Malgorzata Tracz from the Polish Green Party told DW that despite alerting authorities about the ecological catastrophe on the Oder, Polish government institutions did not even warn residents that they should not touch the river water.
She said that around eight tons of fish were found near Olawa alone. “The problem is huge,” she said. “It is not something that can be ignored or that will be overcome on its own.”
The local fishing community “are terrified by the situation,” she noted, saying that anglers have been most vocal on the issue in Poland due to the lack of support from public institutions.
Tracz has written emails to local and federal water and environmental agencies and ministries asking them to investigate the source of the contamination, and to “punish the people that did it.”
So far, she has received no response, despite what she described as “an environmental disaster.”
Tracz said that “there are many theories” about the cause of the fish kill and wants an in-depth investigation.
Polish anglers who rely on the Oder ‘are terrified by the situation’
German campaigners demand water protection
German environment groups are blaming insufficient water conservation measures for the die-off, as well as a lack of cross-border cooperation on the frontier river that crosses the Czech Republic, Poland and Germany.
“This ecological catastrophe would not have been of such magnitude if the German and Polish authorities had worked together more intensively,” said Antje von Broock, managing director of the German Association for the Environment and Nature Conservation (BUND), adding that targeted warnings should have been put in place.
“Dead fish have been floating on the Oder since the end of July, now over a distance of several hundred kilometers,” she said in a statement.
A “diverse and healthy ecosystem” could better resist toxic substances in the river, if they were responsible for the die-off, von Broock added.
“The fish kill is therefore also a symptom of decades of poor planning in water management and chronic underfunding of water protection.”
Both BUND and Malgorzata Tracz said the International Commission for the Protection of the Oder, a joint agreement between Poland, the Czech Republic and Germany to protect one of Europe’s more pristine waterways, needed to be upheld.
Edited by: Jennifer Collins
This story was first published on August 12. It was updated on August 15 to include the latest information on the investigation into the die-off.
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Article source: https://www.dw.com/en/mysterious-mass-fish-kill-in-oder-river-climate-change-or-poison/a-62784099?maca=en-rss-en-ger-1023-xml-atom