Globally, the introduction of non-indigenous species in aquatic environments can threaten indigenous communities by becoming invasive and ecologically dominant. Human-mediated introduction of species is considered one of the main threats to biodiversity and the second cause of extinction for animal species. In Italy, the freshwater fish fauna has been particularly affected during the last decades by introduction of non-indigenous species for angling and aquaculture purposes: on the 82 species present, 38 are non-indigenous (46%). A study was conducted on the fish fauna in 58 lakes in the Trentino province. Forty-seven fish species were recorded from 2001 to 2010, and 18 species (38%) were non-native, representing 5 orders and 8 families. Only 13 lakes have fish communities composed exclusively of indigenous species.