We describe the larval development and voltinism of nine species of running-water dragonflies and damselflies from the upper and middle reaches of the Tordera, a Mediterranean-climate river located in the north-east of the Iberian Peninsula. We sampled larvae between October 2020 and October 2022. We determined larval growth patterns and identified and estimated the sizes of the late developmental stadia by means of correlation graphs between pairs of body features, i.e., head width and hind wing-sheath length, for Calopteryx haemorrhoidalis, C. virgo meridionalis, C. xanthostoma, Pyrrhosoma nymphula, Platycnemis acutipennis, P. latipes, Boyeria irene, Onychogomphus forcipatus unguiculatus, and O. uncatus. Calopteryx virgo meridionalis, B. irene and O. uncatus, characteristic of the upper course, exhibited bifurcations in the timing of their development (cohort splitting), generating patterns of mixed voltinism – 1–2 years per generation in the case of C. virgo meridionalis and 2–3 years in the case of O. uncatus and B. irene. The rest of the taxa, typical of the middle course, were largely univoltine. It is notable that O. forcipatus unguiculatus, hitherto reported as semi- or partivoltine (2–3 years) throughout its range, including the Maghreb, is exclusively univoltine in the Tordera river.