Recent range extensions of the invasive rapa whelk Rapana venosa, biological data of the population and possible ecological impacts on the food webs of the Río de la Plata estuary are presented. A total of 41 rapa whelks and 21 egg capsules were collected between February 2004 and March 2006. Specimens were found all over the mixohaline waters of the estuary, with records off Montevideo, Samborombón Bay and off Punta Rasa. Specimens ranged between 28 and 120 mm shell length. Almost all R. venosa presented epibionts all over the shell, suggesting an exposed lifestyle. Egg-masses were attached to specimens of R. venosa, debris and plastic garbage. The spatial distribution of R. venosa within the estuary was coupled with the spatial distribution of Mactra isabelleana, a typical subtidal bivalve of mixohaline waters. The implications for the food webs of the estuary, including possible predators, are discussed. The presence of R. venosa in muddy sediments together with the finding of egg-capsules over the specimens, and the low salinity values at which it is found in the Río de la Plata estuary, confirmed the high plasticity of R. venosa and the potential capability of successfully invading novel environments.