The life histories of the following species were studied over 2 years at various sites throughout the catchment of the La Trobe River: Tasmanocoenis tonnoiri and Tasmanocoenis sp. (Ephemeroptera : Caenidae), Atalophlebioides sp. and two Atalonella spp. (Ephemeroptera : Leptophlebiidae), two Baetis spp. (Ephemeroptera : Baetidae), Leptoperla primitiva and L. neboissi (Plecoptera : Gripopterygidae), Cyphon sp. (Coleoptera : Helodidae), Ecnomus sp. (Trichoptera : Ecnomidae). The life cycles of these species varied from univoltine (four taxa) to bivoltine (Leptophlebiidae, Baetidae, Ecnomus sp.) or trivoltine (T. tonnoiri). Although the species displayed various degrees of synchrony of growth, distinct changes in the size distribution of the larvae or nymphs occurred with time and thus cohorts were evident.