Open AccessThe extent of freshwater biological invasions is difficult to predict. The thermophilic Daphnia lumholtzi Sars, 1885) (Cladocera: Daphniidae) has successfully invaded a large section of temperate North America from an Old World source, damaging ecosystems and fisheries. The species was later reported introduced into Mexico and Brazil. Here we report D. lumholtzi in Argentina - the most southerly record in the New World for this species. Our genetic analyses establish haplotype identity with North American specimens, consistent with the colonization of South America from North America. The detection dates of the records in South America and the association with the Paraná River, provide evidence that river ways play a role in expansion of D. lumholtzi. The invasion of D. lumholtzi has now reached a similar wide latitudinal span to the distribution in the Old World.