The signal crayfish Pacifastacus leniusculus – called also the Swedish or Californian crayfish, is recorded in Wieprza and Drawa basin. We cannot exclude the occurrence of this species in other waters, especially close to the existing fish-farms, where it could get with farming materials.
Signal crayfishes were imported first to Sweden in the sixties of the XX century, and next to other European countries for farming.
The signal crayfish is significantly larger than the spiny-cheek crayfish and resembles vanishing noble crayfish. Its carapace is even, claws are massive with reddish bottom. Distinguishing feature are white spots in the angle of claws – the kind of „signal”.

Signal crayfishes are very dangerous for European native crayfishes because they are also carriers of crayfish plaque, are highly adaptive and very aggressive.