Astacus astacus (Linnaeus, 1758) is a vulnerable species. Through comprehensive monitoring, we have determined the current spatial distribution of the populations in two streams of the Western Carpathian Massif. In the investigated part of the streams, we did not detect the presence of a source of chemical contamination with hazardous substances causing aquatic animal mortality or significant deterioration of the environmental quality. We sampled at 30 study sites and examined 223 individuals, more than a third of which showed abnormalities, physical damage, body deformation, or the presence of ectosymbionts. External abnormalities were related to the carapace and abdomen; in both sexes, the most frequent were on the claws (amputation, stunting, and mechanical damage); in males, we frequently observed amputation of antennae, carapace damage, or commissural damage; in females, we also found very low egg counts or stunted antennae, deformities of the pleopods, or telson deformities. On the bodies of crayfish, we confirmed the presence of ectosymbionts from the genus Branchiobdella as well.
