Authorities and locals in Basel have raised the alarm after a large number of invasive crayfish were discovered in the River Wiese. The signal crayfish is known to spread rapidly in lakes and rivers and can prove a major threat to local wildlife if left unchecked.

Signal crayfish discovered in Swiss river

Over the past several weeks, locals in Basel started to notice a new and snappy visitor in the streams and ponds of the city. Wildlife watchers took to the internet to report that a large number of crayfish had made a home in the water. “The waters in the Langen Erlen are full. I've never seen them there before,” one wrote.

Speaking to 20 Minuten, cantonal fisheries supervisor Hans-Peter Jermann said “The waters and ponds in the Langen Erlen area are primarily populated by signal crayfish.” First brought to Switzerland in the 1970s to be eaten - before being largely eradicated - signal crayfish have since become “very popular in aquarium keeping, which sometimes leads to them being released by private aquarium owners.”

Signal crayfish are destructive to local wildlife

The species is considered to be highly invasive as they are “not very demanding in terms of habitat and are more competitive than native species, which is very beneficial for their distribution.” Jermann said that the spread of signal crayfish can be devastating for the natural environment, noting that they destroy and displace native plants and animals in their relentless bid to grow the population.

What’s more, signal crayfish carry what is known as the "crayfish plague”, a form of water mould that targets crayfish and can kill them within weeks of infection. “They do not contract the disease themselves, but infect local crayfish populations and therefore have a competitive advantage,” Jermann explained.

Basel attempts to eradicate new crayfish population

For those curious about the two-clawed critter, Jermann warned that “signal crayfish should not be caught, taken away or transported to another body of water.” He confirmed that efforts to contain the signal crayfish - from fishing nets and the introduction of predatory fish to simply fishing them out by hand - are underway, but once settled the crayfish are hard to eradicate.