The life cycles, biomass and secondary production of three sympatric freshwater basommatophoran snails, Lymnaea palustris (MÜller), Physa fontinalis Linnaeus and Anisus rotundatus (Poiret) were studied during two years in a freshwater ditch. L. palustris exhibited an iteroparous life-cycle whereas the two other species presented a semelparous life-cycle, adults died just after oviposition. L. palustris secondary production (dry weight) value was higher (P = 11 298.4 mg 0.1 m−1 yr−1) than those of P. fontinalis (P = 846.3 mg 0.1 m−2 yr−1) and A. rotundatus (P = 1192 mg 0.1 m−2 yr−1).