A benthos-sampling program was carried out in the coastal area of Mar del Plata city in order to know the composition and distribution of infaunal polychaetes living on a subtidal soft-bottom substrate affected by the sewage discharge. Sandy bottoms showed heterogeneous sediment composition and very low organic matter content. Thirty three polychaete species were identified in a range depth between 6.5 to 12.5 m. A comparison with data from 30 years ago from adjacent areas deeper than 12 m is herein presented. Polychaete distribution was related both to the type of sediment and to the content of organic matter. Owenia fusiformis Delle Chiaje was dominant and peaked at stations near the sewage effluent. Small-sized polychaetes were abundant in the sampling area. A possible explanation to the faunal composition of sites near sewage effluents is that hydrodynamic forces frequently disturb the area, and benthic fauna is permanently in an early stage of development. The effect of sewage appeared to be restricted to the shallower subtidal area around the outfall