Piranhas are indigenous to the Amazon basin, in the Orinoco, in rivers of the Guianas, in the Paraguay-Paraná, and the São Francisco River systems.
Aquarium piranhas have been unsuccessfully introduced into parts of the United States.[5] In many cases, however, reported captures of piranhas are misidentifications of pacu (e.g., red-bellied pacu Piaractus brachypomus is frequently misidentified as red-bellied piranha Pygocentrus nattereri).[6] Piranhas have also been discovered in the Kaptai Lake in southeast Bangladesh. Research is being carried out to establish how piranhas have moved to such distant corners of the world from their original habitat. Some rogue exotic fish traders are thought to have released them in the lake to avoid being caught by antipoaching forces. Piranhas were also spotted in the Lijiang River in China.[7]