Summary The purpose of this research was to analyze the abundance and distribution of four recently introduced fish species in the Tiber River basin: Gobio gobio, Luciobarbus graellsii, Rutilus rutilus, and Rhodeus sericeus. An additional aim was to evaluate the relationships of these species with environmental factors. The study area comprised 92 watercourses in the Umbrian portion of the Tiber River basin and analyzed data collected during 1990–2014, in 158 sampling sites. The results show that all four species were quickly established, with self‐sustaining populations revealing invasive characteristics. In just a few years these species extended their distribution significantly in the study area; they preferentially colonized the lower reaches of rivers characterized by warmer waters and a slow current rate and were also associated with poor environmental quality conditions. The research results provide valuable information useful for risk assessment as well as for the design of proper invasive species management programs.