Faxonius limosus
Spot American Crayfish in Switzerland's lakes, Canada's Great Lakes, and Southern Germany. Cold-water crustacean logged across Europe and North America.
Look for a lobster-shaped crustacean with a reddish-brown to olive-grey carapace (the hard shell covering the head and thorax), large forward-pointing claws, and long, whip-like antennae. A distinctive red patch or tubercle (small bump) on the underside of the claw joint is a reliable field mark separating it from native European species. In the water it typically walks slowly across silty or rocky substrate, claws slightly raised.
Typically encountered walking deliberately along the bottom, silty lake floors, gravel beds, or among submerged roots and rocks, often tucking into crevices when approached. It tends to hold its ground or back away slowly rather than fleeing, making patient observation straightforward. Most sightings happen in shallow to mid-depth freshwater where light and visibility allow bottom-scanning.
Originally from eastern North America, this species has spread widely through European river systems, where it outcompetes native crayfish and carries crayfish plague, a water mould that is lethal to European species but does not affect it.
There is no clear seasonal peak in the sighting data, so it can be encountered year-round. Observed water temperatures range from roughly 3 °C to 19 °C, which matches the cold-to-cool freshwater lakes and rivers where it lives across central Europe and North America.
Most commonly logged in Central Switzerland and the Bernese Oberland, where it turns up across a large number of freshwater sites. Strong sighting records also exist across the Great Lakes region of Canada and in Southern Germany and Carinthia's lake district in Austria. France's Alps and Zeeland in the Netherlands round out the European spread.
Mapping where American Crayfish is logged…
The strongest dive records come from freshwater lakes in Central Switzerland, the Bernese Oberland, and Southern Germany, with solid populations also logged in Canada's Great Lakes region and Austria's Carinthia lake district. It has also been recorded in the French Alps, the Netherlands (Zeeland), and Belgium.
Sightings are spread across the year with no clear seasonal peak in the data. The species tolerates cold water down to around 3 °C, so it remains active even in winter months in the lakes of central Europe and Canada.
It looks like a small freshwater lobster with a reddish-brown to olive carapace, large claws, and very long antennae. The most reliable field mark is a red or reddish tubercle on the inner surface of the claw joint. No other crayfish commonly found in European freshwater dives shares this combination of colouring and marking.
Adults typically reach around 8 to 12 cm in total body length, though size can vary. In the water they look noticeably smaller than a lobster but larger than a shrimp, with claws that are proportionally hefty compared to the body.
No. They pose no threat to divers. They may pinch lightly if handled, but the nip is harmless. Observe from a short distance and they will carry on foraging without concern.
This North American species was introduced to Europe in the 19th century, initially for aquaculture, and has since spread through river networks across central and western Europe. It carries a water mould known as crayfish plague that devastates native European crayfish species, which is why it now dominates many of the freshwater sites where divers encounter it.
Site and sighting data is aggregated from diver logs, iNaturalist and GBIF. For taxonomy and conservation status:
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