This paper describes the first discovery of Sinanodonta woodiana and S. lauta in the artificially heated section of the Reft Reservoir (Sverdlovsk oblast, Reft River, Ob–Irtysh River basin). The discovered Sinanodonta populations are represented by invasive haplotypes E3 (S. woodiana) and C3 (S. lauta). The alien populations include S. woodiana and S. lauta individuals belonging to various size and age groups, which indirectly indicates the successful naturalization of these species. Old-aged individuals (over 10 years) predominate in the S. woodiana population (56%), while middle-aged ones prevail in the S. lauta population (48%). Sinanodonta individuals under 1 year old (shell length less than 25 mm) were not found, and specimens aged 2–3 years occur rarely. On the basis of the molecular data and archival fishery records, it can be assumed that this invasion of S. woodiana and S. lauta into the Reft Reservoir is associated with the introduction of commercial fish species from Volga fish farms at the end of the 20th and the beginning of the 21st century.