It adapted to new conditions very quickly and expanded through the streams of 27 European countries. It was named after the blue, intensive spots on the pincers between the fixed and movable finger, making it most distinguishable among our native species of crustaceans. Today, the signal crayfish is one of the biggest threats to the survival of indigenous species of crustaceans. In addition to direct competition for food and habitat, signal crayfish also transmits fungus, which causes crayfish plague, which has been ranked among 100 most dangerous invasive species of the world, to which it is resistant. By further expansion to karst streams, signal crayfish would have a strong negative impact on endangered and strictly protected species of native crayfish, but also on the entire freshwater ecosystem. In addition to extremely adverse environmental impact, this species inflicts economic damage by building shelters on the banks of the watercourses, thus causing their collapse.