Despite fishermen removing rotting carcasses of fish, birds, beavers, and other wildlife for weeks in the Polish section of the Oder River, the government did not inform the public until Friday, August 12, 2022. The Polish Prime Minister did not notify Germany of the situation even as the toxic river water entered their shared border of 124 miles, which eventually flows through the river delta to the Baltic Sea.

Today, yet another mass mortality event, this time in Frankfurt. The first deaths in the Baltic sea have been confirmed.

Weeks ago, Prime Minister Mateusz Morawiecki announced that someone had deliberately poisoned the river with toxic chemicals and vowed to find the perpetrators and punish them accordingly.

But the harmful chemicals that could have caused such damage as mercury (with only one possible source, river dredging) and the solvent mesitylene  have now been ruled out by laboratory tests as the source of the wildlife kill.

Instead of chemicals, researchers discovered elevated levels of salinity and believe climate change has had a significant role. 

Hunger Stone: The recent droughts in Europe have made visible the "Hunger Stones" in some Czech and German rivers used to mark desperately low river levels that would forecast famines. This one, in the Elbe river, is from 1616 and says: "If you see me, cry". from History Review pic.twitter.com/mrVYTVyvLx

Anna Moskwa, the minister of climate and environment, said analyses of river samples taken in both Poland and Germany revealed elevated salt levels. Comprehensive toxicology studies are still underway in Poland, she said.

She said Poland's state veterinary authority tested seven species of the  dead fish  and ruled out mercury as the cause of the die-off but was still waiting for results of other substances. She said test results from Germany had also not shown a high presence of mercury.

The Washington Post noted that climate change worsened the situation.

Scientists have speculated that factors beyond deliberate dumping could be at play. The mercury could have settled in the river’s sediment because of past pollution, before being stirred up by recent dredging. Europe’s  historic heat wave this summer  could also be to blame. The continent is facing what is potentially its worst drought in 500 years; low water levels and high temperatures could be choking off oxygen supplies to the river’s aquatic life and worsening existing pollution.

“This is a problem we will increasingly face as we move into a world affected by climate change. Pollutants that are out there are more toxic because they are present in higher concentrations during drought conditions,” said David Taylor, a professor of environmental change at the National University of Singapore.

“We are in this strange period now, where we are beginning to see, more and more, not just the direct effects of climate change, such as droughts and storms, but also the knock-on effects of climate charge.”

Christian Wolter, researcher at the department of fish biology, fisheries and aquaculture at the Leibniz Institute of Freshwater Ecology and Inland Fisheries, said that ongoing dredging to deepen the river channel might have released embedded mercury.

"The only source of mercury in the Oder River is the bottom sediment which is known to be enriched in mercury from past pollution," he told DW.

But he also believes the problems on the Oder run deeper.

Fish in the river are struggling, Wolter 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 — a rigid structure 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.

Politico on the Polish election as the disaster plays out, will Tusk get a boost from the disaster in the election?

To hear Donald Tusk tell it, he’s gone back to Warsaw with a mission : to save the European Union. The former Polish prime minister and European Council president has launched a national comeback effort, targeted at toppling a government that is increasingly at odds with Brussels and flirting with all-out war against the bloc’s system of governance.

Tusk, 64, has faced his fair share of political challenges. He grew up in Gdańsk during the port city’s tumultuous uprising against communism, led Poland through the financial crisis and presided over the Council during its migration and Brexit dramas. His next battle is arguably just as important — and more personal — as any of those.

Poland’s governing Law and Justice (PiS) party has carried out a demolition job on judicial independence and put the country on a collision course with the rest of the EU through a challenge to the supremacy of the Court of Justice of the European Union. While a Polexit remains unlikely, the drama with Warsaw is nevertheless a drag on the Brussels agenda, sucking attention away from broader priorities. The fight also risks spilling out into other areas of EU policymaking: climate targets, budget spending and migration policy.

Construction works at #Oder/#Odra river needs to be stopped immediately by Polish authorities. Ongoing construction violates EU legislation and adds even more stress to fish & the entire river after the ecological disaster. @VSinkevicius @MorawieckiM https://t.co/BRrbDanMI1

Minutes ago, the AP reported Germany called the event an ecological catastrophe.

The disaster is only one example of myriad adverse environmental events threatening the world's food and water security.

“So far, at least 150 samples of water from the Oder River have been tested. None of the studies have confirmed the presence of toxic substances. At the same time, we are testing fish. No mercury or other heavy metals have been found in them,” she said.

She said some Oder water samples were being sent to foreign laboratories to be tested for about 300 substances.

Both ministers said they were focused now on doing what they can to limit the damage to the river’s ecosystem.

Lemke suggested that German authorities were not alerted quickly enough after dead fish were detected in Poland and said communications between the two countries should be improved.