Fisherman Claude Delley rattles the metal frame of his net against the side of his boat on Switzerland’s Lake Neuchatel, trying to shake off dozens of tiny, brown mussels.
Some plop back into the water but most stay put. The sharp shells of the creatures – a fast-spreading, invasive species originally from the Black Sea – work away at the netting, meaning he has to replace it twice as often as before.
“There is no solution,” he said. “As soon as the mussel clings to the net, it stays there.”
It is not just the nets. The Quagga mussels have clogged up underwater pipelines. Stéphan Jacquet, one of a team of researchers studying the species, said he had seen Swiss native crayfish, whose population is in decline, encrusted in the creatures, threatening suffocation.
The mussels also consume huge amounts of microscopic plants called phytoplankton, leaving less for other lake creatures to eat.
“Potentially all biological categories and major links in the food chain can be impacted,” Jacquet, who works at the INRAE CARRTEL laboratory further south in Thonon-les-Bains, said.
The mussels were first detected in Switzerland in the River Rhine near Basel in 2014. Since then they have spread to colonise at least six Swiss lakes including Lake Geneva.
The population, which has few predators, is poised to multiply up to 20 times in Switzerland in the next two decades, according to a 2023 study by aquatic research institute Eawag and Swiss universities based on trends seen in the Great Lakes of the United States since the 1980s.
The mussels are already present in France and Germany.
It is not known exactly how each lake was invaded, but mussel larvae can spread on rivers or currents and be introduced into new bodies of water when boats or equipment are moved.
Once in, the species multiplies rapidly with one individual capable of producing hundreds of thousands of larvae.
“When we look underwater, we can see that it has an exponential colonisation, very significant, as these ecosystems are now completely covered, from the surface to the depths,” Jacquet said.
Some Swiss lakes have been spared, including Lake Zurich and Lake Lucerne. In some places, authorities are now considering new rules for cleaning and shipping boats to stop the spread.