Lake Zurich's Long History of Invasion

A lake under pressure

Lake Zurich is a drinking water source for over 1.3 million people and a recreational lake for millions more. What most visitors don’t see is the benthic community, the invertebrates living on and in the sediment of the lake floor. Today, non-native species account for 85% of all individuals in the shallow Lower Lake. The community is no longer primarily native. It is an assembled mixture of species from across the globe, most of which arrived unintentionally.

The timeline of arrivals spans more than 100 years.

The arrivals

~1978: New Zealand mudsnail (Potamopyrgus antipodarum)

Tiny, just a few millimetres, and capable of reproducing without males. This snail spread rapidly through European waterways via boat traffic and waterbird movements. In Lake Zurich’s Lower Lake, it once reached nearly 29,000 individuals per square metre. Recent surveys found only ~676 ind. m⁻², a ~43-fold decline, likely driven by competition with later arrivals.

~1978: Zebra mussel (Dreissena polymorpha)

Native to the Ponto-Caspian region, introduced to Western Europe via ballast water. It filter-feeds intensively, encrusts hard surfaces, and quickly became the dominant bivalve of European lakes. In the Lower Lake today, densities average ~10,000 ind. m⁻², an 88-fold increase since its first detection. It currently dominates the benthic community.

~1985: Signal crayfish & Rainbow trout. Both from North America, introduced deliberately for aquaculture and sport fishing. Crayfish introductions are particularly damaging: they disturb sediment, predate invertebrates, and outcompete native crayfish, which are now largely absent.

~2000: Killer shrimp (Dikerogammarus villosus)

Also from the Ponto-Caspian region. One of the most aggressive freshwater amphipods in Europe: it attacks and kills prey it does not even eat, including native invertebrates, small fish, and other invasive species. Its arrival marked a broader wave of Ponto-Caspian invaders moving westward through European river networks.

~2010s: Asian clam, Rockpool shrimp, North American amphipod. Each adding another layer to an already heavily invaded community.

The latest arrival: Quagga mussel

In September 2024, during my own benthic field surveys, I found the Quagga mussel (Dreissena rostriformis bugensis) in Lake Zurich, the first confirmed record. Like the Zebra mussel, it originates from the Ponto-Caspian region and arrived in Western Europe via ballast water. It first appeared in Switzerland in Lake Constance in 2014.

The Quagga mussel is considered even more ecologically impactful than the Zebra mussel: it tolerates deeper water, softer sediments, and can reach extraordinary densities. In Lake Constance, established populations already reach ~8,000 ind. m⁻². In Lake Zurich today, densities are still low, between 28 and 74 ind. m⁻². The invasion is in its early stages. But history suggests what comes next.

The full picture

Looking at a century of arrivals together, a pattern emerges. The most impactful species, Zebra mussel, New Zealand mudsnail, Killer shrimp, and Quagga mussel, share the same origin (Ponto-Caspian region) and the same pathway (shipping and waterway connectivity). They are ecological generalists that thrive in disturbed, invasion-saturated conditions.

The Quagga mussel is not the end of this story. It is the latest chapter.

The invasion chronology is based on first records in the Lower Lake compiled from AWEL (Amt für Abfall, Wasser, Energie und Luft, Kanton Zürich), Burla, H. & Ribi, G. (1998). Population density of the snail Potamopyrgus antipodarum in Lake Zurich. Aquatic Sciences 60(1), 33–39, and InfoFauna – Centre Suisse de Cartographie de la Faune (infofauna.ch).