A sampling programme was devised to assess in terms of 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD) and suspended solids (SS) removal the performance of one anaerobic, one facultative and two maturation ponds in series, for treating the wastewaters resulting from a slaughterhouse killing approximately 625 pigs/week. The results show that, in spite of poor maintenance,which has been causing bank erosion and macrophyte infestation, the system has coped with large variations in flow and organic load, reducing to a minimum the impact of the effluent discharge on the receiving creek.