After the massive fish kill in the Oder, environmentalists and scientists are again calling for the river to be stopped immediately.
"The expansion measures are not up to date in a river ecosystem that has pronounced low water phases," said Florian Schöne, Managing Director of the German Nature Conservation Ring, on Friday.
Poland is unilaterally expanding the Oder into a faster waterway.
Kim Maurus
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The water in a straightened river flows off too quickly and exacerbates the low water, explained the water ecologist Christian Wolter.
In a natural river, the spring floods fill up the reservoirs of the floodplains, which hold and filter the water for a long time.
It is important to give the river more resilience through renaturation, also against climate change.
"Climate projections predict that we will have more of these low water periods," Wolter said.
Researchers had identified an alga in the Oder that is poisonous to fish and molluscs and prefers to live in dammed brackish water.
It was therefore able to multiply greatly due to low water, the barrages in the Oder and a massive discharge of salt.
Wolter assumes that up to 1000 tons of fish died in the Oder.
So far, only about 200 tons have been recovered, most of which have sunk to the bottom of the river.
Bacteria now decomposed this biomass and consumed the oxygen in the water.
This could be dangerous for the still living fish.
"It will only be possible to take stock in the next two to three weeks."
The German-Polish Environmental Council will meet on Monday to discuss the fish kill.
BUND environmentalist Sascha Maier said the meeting was an opportunity to "build a seed of trust."
The work of the International Commission for the Protection of the Oder against Pollution, the members of which are Poland, the Czech Republic and Germany, must be improved.