In this work, the serotypes of Salmonella genus polluting the waters of Lujan River, situated in the north east of the province of Buenos Aires, Argentina, were studied. A total of 690 samples of water were collected and analysed from February 1988 through December 1989, at three different sites. They were obtained according to the Moore technique and then preenriched in buffered peptone water and enriched in Rappaport-Vassiliadis Soya peptone broth was carried out. The isolations were realised in brilliant green-desoxycholate agar and bismuth sulphite agar and the presumptive colonies to be Salmonella were tested by the standard biochemical identification. Salmonella spp. was isolated in 434 samples (62.9%). The predominant serotype was S. Anatum, followed in a decreasing order by S. Montevideo, S. Newport and S. Bredeney. A large amount of serotypes that are isolated with very low frequency and very rarely in other hidric courses in the country were: S. Westhampton, S. Poona and S. Saintpaul were found.