The Haliacmon (Modern Greek: Αλιάκμονας, Aliákmonas; formerly: Ἁλιάκμων, Aliákmon or Haliákmōn; Slavic: Бистрица, Bistritsa;) is the longest river in Greece, with a total length of 322 km (200 mi).(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).
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 Polyfytos. Southeast of Veria, the Haliacmon enters the central Macedonian plains, an area of great importance to agriculture. It flows into the Thermaic Gulf west of the delta of the Axios (Vardar), northeast of the coastal town Methoni.
In antiquity, Claudius Ptolemy called the chain of mountains in which the river rises (northern Pindus) the Canalovii. According to Julius Caesar, the Haliacmon formed the line of demarcation between Macedon and Thessaly. In the upper part of its course it took a southeast direction through Elimiotis, which it watered; and then, continuing to the northeast, formed the boundary between Pieria, Eordaea, and Imathia. In the time of Herodotus the Haliacmon was apparently joined by the Loudias 7, 127, the discharge of the lake of Pella; but a change has taken place in the course of the Loudias, which no longer joins the Haliacmon, but flows directly into the Aegean Sea. The image below shows a wind gap between the Haliacmon and Loudias watersheds that is the probable ancient course of the Haliacmon.
It was the domain of the eponymous river god Haliacmon.
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