Oder-Fischer Andre Schneider can’t get this picture out of his head. His daily view of the calmly flowing river and then last year’s hot August day when suddenly a huge carp drifted by.

“It was the moment when the fish first turned and then rolled its eyes, as if to say: Now help me,” recalls the 39-year-old. What he didn’t suspect at the time: It was soon to get much worse.

Countless fish die in the summer of 2022 in the Oder – lead, roach, carp, zander. Germany’s only floodplain national park is also in danger. Experts assume that high salinity, low water, high temperatures and the toxin of the algae species Prymnesium parvum were the causes of the fish deaths.

Another mass extinction possible at any time?

One year later. Significantly excessive salt loads are still being measured in the river. So far there hasn’t been another mass extinction, but will it stay that way?

Lots of rain causing rivers to swell and lower temperatures can mean there is less chance of a major algal bloom. “It’s possible that a lot of the problems will be swept away and we’re lucky this year,” says fish ecologist Christian Wolter from the Leibniz Institute for Freshwater Ecology and Inland Fisheries (IGB).

However, experts continue to see risks for late summer and the coming years if the heat and low water levels offer the toxic golden alga good conditions for mass reproduction.

“The entire ecosystem of the Oder is still badly damaged after the environmental disaster in the summer of 2022,” says Federal Environment Minister Steffi Lemke (Greens). “Local fish kills in Poland in a reservoir and most recently in June this year in the Gliwice canal system show that the danger has not been averted, even if the situation in the Grenzoder in Germany currently gives no indication of a possible fish kill,” says the Federal Environment Ministry .

Salinity very high – mystery about golden algae

The values ​​for the salt content in the Oder are still reaching dangerous levels: On August 4th, for example, an electrical conductivity of 2340 microsiemens per centimeter was measured at the measuring point in Frankfurt (Oder) as an indicator of this. A year ago, the figure had risen to over 2,000.

According to Wolter, it should actually be around 600 to 700. “Symptoms are combated, but nothing is done about the causes,” says the scientist one year after the environmental disaster. Environmental organizations and Federal Environment Minister Lemke assume that the high salt content is probably due to wastewater from the Polish mining industry.

The Oder then became a deadly cocktail for many fish last year, because a still rather mysterious type of algae multiplied and produced correspondingly more poison. Researchers want to clarify from which salt value and under which conditions mass reproduction of this alga occurs. “I hope that we will be smarter next year,” says IGB water ecologist Jan Köhler.

In the Lower Oder Valley National Park, the development of golden algae in the polder waters is regularly monitored. So far, very low concentrations have been detected, says director Dirk Treichel. But the river has been missing an important support since the disaster: According to Treichel, around 65 percent of the large mussels died in the summer of 2022. They filter the water, ensure transparency. Now the river looks conspicuously cloudy due to suspended matter and algae. The bottom is partially covered by a 20 centimeter thick layer of mussel remains.

How are the fish in the river?

According to estimates, more than half of the fish that had previously lived in the river were missing in the course of the Oder disaster. According to estimates by the IGB, the weight of the fish that died last summer totaled up to 1,000 tons. The ray of hope: The populations can recover, the reproductive conditions are good according to experts. “I’m in very good spirits at the moment, because there are also a lot of young fish,” says Fischer Schneider.

What is happening to protect the Oder?

There are different attitudes in Poland and Germany as to what therapy for the wounded river might look like. The Federal Environment Ministry has been in contact with the neighboring country since last year, but the relationship remains tense. There were workshops, conferences and Lemke’s constant call to her Polish counterpart to significantly reduce salt discharges. The German warning and alarm plan for the Oder was revised and river monitoring improved. According to Poland, Poland is also monitoring the water values ​​more intensively.

The Oder expansion remains a bone of contention. On the Polish side, the state water management company Wody Polskie is pushing ahead with the expansion and has not been stopped by several court decisions. On July 21, a district court ordered prosecutors to investigate the building inspectorate of the Lubusz Voivodeship. Because they do not want to enforce a court-imposed building freeze.

“It’s a kind of victory for the NGOs and lawyers against the government’s policies,” said environmentalist Radoslaw Gawlik of the Wroclaw-based organization EKO-Unia. Nevertheless, he has little hope that the work will be stopped.

The commitment of environmentalists for the Oder and the reporting about it are a thorn in the side of the leadership in Warsaw. The government representative for information security, Stanislaw Zaryn, saw campaigns controlled from Germany at work. They served to “exercise pressure contrary to the interests of the Republic of Poland,” he said in Warsaw.