A B S T R A C T. - The present study contributes to the knowledge about the distribution of the scattered and scarce populations of the threatened Iberian endemic fish species, lamprehuela (Cobitis caldero n i Bacescu, 1961) within the Ebro River basin. The Erro River was thoroughly surveyed to: 1) identify and describe reaches with suitable habitat, and 2) to elaborate a detailed distribution map in order to give conservation recommendations for the species within this protected area. The length-weight relationship (a = 0.0018, b = 3.3972, r 2 = 0.9483, p < 0.0001) as well as mean Fulton’condition factor (K = 0.3477, SE = 0.0083) for C. caldero n i, and its occurrence in the Irati and Ega Rivers (Ebro River basin) are reported here for the first time.