An employee at the Wild Salmon Centre examines a salmon that shows bite marks.
"FIIISH!" shouts Dennis Bock over the roar of the weir. He quickly dips his landing net into the dark green water.
Moments later, a powerful, muscular creature wriggles in the hands of the 48-year-old fish farmer: a beautiful wild salmon.
Almost 80cm long, sporting a shimmering brownish-red and orange spawning dress, fish like these normally flourish in the vast wilderness of Alaska.
But this one was fished from a tributary of the Sieg and Rhine rivers, less than 30km from the western German city of Cologne.
To the Arctic and back
The wild salmon now laying in a tub next to Bock is part of a state migratory fish programme, an attempt to bring a piece of real wilderness back to the Rhine, once the largest salmon river in Europe.
"We probably released this one as a smolt three or four years ago," says Bock's colleague Sven Wohlgemuth from the Rhine-Sieg Wild Salmon Centre.
Since then, the fish has travelled down the Rhine to the North Sea and on towards the Arctic where, off the coasts of Greenland, Iceland or Norway, it stuffed itself with herring until fully grown, he says.
After a few years in the ocean, the salmon then makes its way home to its spawning habitat, to reproduce in the shallow gravel in November or December.
It is an arduous journey. Salmon travel between 3,000km and 5,000km, passing sharks, seals, weirs and rotating ship propellers. Only one in more than 3,000 juvenile salmon makes it back.
"Sometimes I wish the salmon could write books, there are so many stories they could tell us," says Wohlgemuth.
He points to a dark, horseshoe-shaped imprint on both sides of the freshly caught fish. "A catfish bite."
Repopulation efforts suffer setback
Salmon became extinct in Germany in the 20th century due to pollution, blocked waterways and overfishing.
Since the 1990s, efforts have been made to resettle the species, especially in the Rhine, Elbe and Weser rivers.
Obstacles such as dams and hydroelectric power plants have been equipped with fish ladders – structures to facilitate fish migration.
A number of returning salmon are plucked from the water each year to hatch hundreds of thousands of young from their eggs and release them into the rivers in spring.
The launch of programmes aimed at supporting fish migration has led to a significant increase in the number of salmon returning to their spawning grounds.
The Siegburg Wild Salmon Station on the Sieg river reported an average of 200 returnees in the Rhine tributaries in the state of North Rhine-Westphalia every year since the turn of the millennium, counting over 500 in 2007.
The measures have also been successful on the Elbe river, according to data from the North Atlantic Salmon Conservation Organization.
Researchers assume that only about a third of the returnees are recorded.
But when Germany was hit by drought in 2018 and 2019, numbers plummeted nationwide and have not recovered since.
In 2024, only 72 returning salmons have been counted so far in North Rhine-Westphalia, where the highest numbers of salmon are caught in Germany.
"Water levels have simply been far too low since 2018," Wohlgemuth explains.
Low water levels not only make migration more difficult but also mean the fish are more vulnerable to predatory fish and cormorants, which have an easier time to feast on them at bottlenecks such as fish ladders.
Long-term resettlement
Nevertheless, the situation is not hopeless, says fish ecologist Christian von Landwust from the Federal Institute of Hydrology.
It is possible to reintroduce salmon to Germany in the long term, he says, but to achieve this, existing efforts will have to be significantly intensified.
Instead of adding fish ladders, waterways need to be made passable over longer distances and dams dismantled, von Landwust says.
Salmon looking to travel up the Rhine encounter the biggest obstacle right at the start, in the Rhine delta in the Netherlands, says the ecologist.
Only one arm of the Rhine is completely open here, while the others are often blocked by gigantic barrages, the Haringvliet locks.
A few years ago, the Dutch government issued a decree stipulating that the lock gates have to be opened regularly to promote fish migration, giving the salmon more time to pass through and adapt from salt to fresh water.
"Of course, it's not just about the salmon," says Wohlgemuth. "Everything we do for the salmon also benefits other fish species."
Restored waterways benefit the entire aquatic community and humans benefit too. Not only can clean drinking water be obtained from intact salmon waters, but they also protect against flooding.
Floodplains, for example, act as buffer zones and store excess water.
The male wild salmon in Bock's hands has reached its destination, but instead of looking for a mate in a small tributary, it is now lying in a plastic tub.
The fish farmers quickly note down the last data and then take the fish to the breeding station where they will select a suitable mate based on genetic analysis.
Experts believe that without human assistance, too few fish would find a mate on their own in the gravelly riverbed. "But if we do end up without a job one day," says Wohlgemuth, "then we'll know we did the right thing." – By MAXIMILIAN VON KLENZE/dpa