Aims To investigate Norovirus (NoV) contamination of mussels, clams and oysters harvested in two class B harvesting areas of the delta of the Po river, to choose a species as an indicator. Methods and Results Environmental parameters (temperature and salinity) and hydrometric levels of the tributary river were measured. Seventy shellfish samples (35 samples per area) were examined for Escherichia coli and NoV (GI and GII). NoV contamination was found in 51.4% of samples, of which, 2.9% contained only NoV GI, 14.3% only NoV GII, while the majority of the samples (34.3%) contained both genogroups. Most of the positive results (90.0%) were obtained in the period between November 2008 and April 2009. Conclusions No significant differences were found between the results from the two harvesting areas and the three shellfish species. However, on the basis of the average Ct values, the recovery rate (from 0.46 to 1.15%) and the distribution of positive results in the samplings, mussels seem to be a suitable indicator species to monitor viral contamination in these areas. Significance and Impact of the Study The data allow the optimization of monitoring plans to improve the prevention strategies in terms of money and time, by the intensification of controls in the cold season and the use of one species as indicator.