Switzerland has three native crayfish species, Austropotamobius torrentium, Austropotamobius pallipes and the noble crayfish Astacus astacus. Four introduced species are living in Switzerland: Astacus leptodactylus from Turkey and three American species: Orconectes limosus form strong populations in the western part of Switzerland and are spreading eastwards. O. limosus may have displaced A. pallipes from many places. The signal crayfish Pacifastacus leniusculus has been found in the Lake of Geneva and in some smaller lakes. In Sweden, the signal crayfish has locally displaced the noble crayfish. Therefore the signal crayfish may threaten the indigenous crayfish species of Switzerland. The red swamp crayfish Procambarus clarkii is thriving in three ponds in the northern part of Switzerland. It has reached high population densities in other parts of Europe, especially Spain. It's potential to colonize Swiss lakes is presently unknown. All three American species are vectors of the crayfish plague Aphanomyces astaci which has caused severe damage to endemic populations in Switzerland.