How the Quagga Mussel Was Found in Lake Zurich

When the Quagga mussel (Dreissena rostriformis bugensis) made headlines in autumn 2024, the coverage focused on what would come next: boat-cleaning rules and launch bans. What received less attention was the discovery itself: a quiet afternoon at a Zurich lakeshore, a handful of small mussels, and the gradual realisation that something had changed.

Here is that story.

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A routine sampling trip

In September 2024, Jukka Jokela (Eawag) was snorkeling at Mythenquai, a public bathing area on the western shore of Lake Zurich, collecting benthic samples at 1 m depth. This was part of the benthic community survey of Lake Zurich, the same survey that forms the foundation of my first PhD project. Nothing about the day suggested it would be unusual.

Among the material collected were small mussels that didn’t look quite right for Zebra mussels (Dreissena polymorpha), which had been present in Lake Zurich since the 1970s. The shells were rounder and lacked the characteristic angular keel of the Zebra mussel.

Lars Sturm, then working at Eawag and now a PhD student at Simon Fraser University, examined the specimens and made the first identification: Quagga mussels.

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Confirmation

Visual identification of Dreissena species can be uncertain: the two species overlap in shell morphology, and juveniles are particularly difficult to distinguish. The specimens were passed to lab technician Marco Giulio (Eawag), who confirmed the identification using COI barcoding, a standard DNA-based method that uses a short, diagnostic segment of the mitochondrial cytochrome oxidase I gene to identify species with certainty.

The result was unambiguous. The mussels were Dreissena rostriformis bugensis, the Quagga mussel. The first confirmed record in Lake Zurich.

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The response

The cantonal authorities (Kanton Zürich) moved quickly. Within days, the findings were made public and a launch ban was imposed on several other lakes in the canton specifically Greifensee, Pfäffikersee, and Türlersee, as a precautionary measure to prevent further spread via recreational watercraft.

Boat cleaning is now central to the management response. The SMRP (Schiffsmotoren-Reinigungspflicht), mandatory boat cleaning requirements in the canton of Zurich, targets precisely the pathway by which species like the Quagga mussel move between water bodies: on and in the hulls, motors, and equipment of recreational boats. Quagga mussel larvae and juveniles are microscopic. They are invisible to the naked eye and survive for hours in residual water. Cleaning, draining, and drying watercraft between launches is the most effective measure currently available.

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What comes next

The Quagga mussel was first detected in Switzerland in Lake Constance in 2016. By 2024 it had reached Lake Zurich. In Lake Constance, established populations now reach densities of around 8,000 individuals per square metre. In Lake Zurich at the time of discovery, densities were between 28 and 74 individuals per square metre.

The invasion is in its early stages. The ecological trajectory of this species in Lake Zurich, and what it means for the benthic community already dominated by invasive species, is exactly what my PhD research is designed to track. How the Quagga mussel is spreading and adapting genetically across Swiss lakes is the focus of my second PhD project on invasion genomics.

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In the media

Gewässer in Gefahr: Invasion der Quaggamuschel – das können wir dagegen tun (SRF Wissen, December 2024)