Toxic species of algae found in the Oder

Helpers are fetching tons of dead fish, mussels and snails from the border river Oder. After initially suspecting a chemical spill, it now looks like another cause: a massive growth of algae that was promoted by a Polish ore mine.

Tons of zander, catfish, gudgeon and loach, as well as mussels and snails have died in the Oder. However, researchers hope that some have survived and will soon breed again.

Sean Gallup/Getty

“We definitely rule out a chemical accident,” says Christian Wolter from the Leibniz Institute for Freshwater Ecology and Inland Fisheries, who took a close look at the mass death of fish and mussels in the Oder. On the other hand, the ecologists are now looking at a type of algae that must have multiplied massively in the Oder in recent weeks. The researchers found the microalgae Prymnesium parvum in very high concentrations in their water: “There were 100,000 algal cells in one milliliter of diluted water,” says Wolter.

This type of algae is normally only found in brackish water, i.e. in a mixture of salt and fresh water, such as that found in estuaries – but not in the entire river. The algae also need a very high pH value in the water. She can produce a toxin that is deadly to fish and crustaceans but harmless to humans.

“But we won’t be able to say for sure until the middle of next week whether the algae toxin really killed the fish,” emphasizes Wolter. Extensive research is needed to prove this.

A mine emptied the brine pools

However, many indications support the algae theory: The fact that this type of algae was able to thrive in such large numbers in the Oder speaks for a high salt supply from outside. In fact, the water ecologists working with Wolter were able to measure an unusually high salt content in the water and also a high pH value. In addition, at the point where the fish kill was first observed, there is a damming and the water flows particularly slowly. Nearby – in Eisenhüttenstadt – the water level suddenly rose by 30 centimeters and more.

And indeed: Yesterday evening the Polish newspaper “Gazeta Wyborcza” reported that between July 29th and August 10th the hydrotechnical plant of the KGHM company drained huge people of salt water into the Oder in the town of Glogow on the Polish side. The company, which operates mines and ores and needs brine basins for this, does this regularly and this time has also been officially approved by the Polish water authorities.

Since the Oder has very low water levels due to the drought, such a huge salt water supply naturally has enormous effects, says Wolter. “How can you approve such a saltwater dump in the summer? That is at least grossly negligent, basically an environmental crime.” It is no longer appropriate to allow such a practice.

No more saltwater dumping in summer

In the course of climate change, the summers would become hotter, and the stress would also increase for the ecosystems in the rivers. “How can you still dump the little water with salt water with a clear conscience?”

The situation is dramatic but not apocalyptic: Wolter and his colleagues do not assume that every living being in the river is dead. Fish have a high reproductive power. This means that a female can produce thousands of eggs and sire that many offspring at once. So stocks will recover.

20,000 young sturgeons are dead

Still, the damage is devastating. For some species, the food chain could initially be interrupted until significant stocks of fish have grown again. “Mussels, for example, need fish as intermediate hosts,” says Wolter. If there are hardly any fish, it will be difficult for them.

The situation is particularly sad as far as the sturgeon is concerned: in the Oder there is a large-scale reintroduction project for the old giant animal, which is one of the most endangered species in the world. “In one of our tanks, 20,000 young animals died, which should soon have been released into the wild.” Very large, dead sturgeons have also been sighted in the river.

It is particularly critical for the sturgeons because they only reproduce when they are between 14 and 20 years old. “So many years of rearing work have been lost for us,” says Wolter.

However, the researchers see a glimmer of hope: The adult sturgeons, which are expected to spawn in the Oder next spring, are currently in coastal waters in the sea. “Perhaps these sturgeons were very lucky and were spared this catastrophe.”

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