The Haliacmon (Modern Greek: Αλιάκμονας, Aliákmonas; formerly: , Aliákmon or Haliákmōn; Slavic: Бистрица, Bistrica;) is the longest river in Greece, with a total length of .(In Greece there are two rivers longer than Haliakmon, Maritsa (in Greek Εβρος) and Vardar (in Greek Αξιός), but the length of each one of them in Greek territory is less than that of Haliakmon, which flows entirely in Greece). Haliacmon is the traditional English name for the river, but many sources cite the formerly official Katharevousa version of the name, Aliákmon. Today, the only official variant is the demotic Aliákmonas. It flows through the Greek regions of West Macedonia (Kastoria, Grevena and Kozani regional units) and Central Macedonia (Imathia and Pieria regional units).