The Haliacmon (, Aliákmonas; formerly: , Aliákmon or Haliákmōn) is the longest river flowing entirely in Greece, with a total length of . In Greece there are three rivers longer than Haliakmon, Maritsa (), Struma (Strymónas), both coming from Bulgaria, and Vardar () coming from North Macedonia, 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). Its drainage basin is . Name The name (in Greek) is composite and derives from (salt, sea) and (anvil). In Greek mythology Haliakmon was one of the Potamoi, who were sons of Oceanus and Tethys, according to the allegorical obsessive-anthropomorphic concept familiar to the Ancient Greeks, on geological upheaval after Deucalion's deluge. An ancient tradition says that sheep that drank water from Haliakmon would turn their colour to white. This tradition is confirmed by the following record of the Roman author Pliny the Elder (23-79 AD) : Similarly in Macedonia, those who want their sheep to be white go to Haliakmon, while those (who want them to be) black (go) to Axios (Vardar). Ottoman Turks called the river Ince-Karasu (narrow-black water), a name still used in Turkey. The Eastern South Slavic name is Бистрица, Bistritsa which is still in use in Bulgaria and North Macedonia. Course and tributaries Before the construction of its diversion dam near the village of Aghia Varvara in the mid-1950s, Haliakmon had no permanent river bed in its lowland course. It often flooded and formed extensive marshes. Its devastating fury in December 1935 remains fresh in memory of the elder inhabitants of the region (Veria and Alexandreia). The Haliacmon rises in the Gramos mountains in northern Greece, near the border with Albania. In its upper course it flows generally towards the east, and turns southeast near Kastoria. It describes a wide curve around the Vourinos mountains, and turns northeast near the village Paliouria. It feeds the large artificial lake Polyphytos, that was created after the construction of the namesake hydroelectric dam and consists almost its entire course through the Kozani prefecture. Over the