river, the longest in Greek Macedonia. The river's total length is 185 miles (297 km). Rising in the Grámmos Mountains of the eastern Pindus Range on the Albanian frontier, the Aliákmon River flows southeast through gentle valleys and basins and is joined by a tributary, sometimes also called the Aliákmon, which rises near the Albanian border. After collecting the drainage of Lake Kastorías, its flow is confined to narrow gorges during much of its middle course along the base of the easternmost Pindus. Near Siátista it receives the Pramorítsa River and, farther south, the Venétikos. Swinging around the southern end of the Voúrinos Mountains, the Aliákmon is forced into a wide loop toward the northeast by the northeast–southwest-trending Kamvoúnia massif.

Emerging from between the Vérmion and Piéria mountains, the Aliákmon traverses the Thessaloníki (Salonika) plain, through which it apparently was navigable by small ships in the Middle Ages; but today a hydroelectric dam south of Véroia is a barrier to river traffic. Near Véroia the Aliákmon is joined by a last tributary, the Moglenítsas, which drains the entire western Thessaloníki plain; together they debouch into the upper Gulf of Thérmai on the Aegean Sea. Formerly called by its Macedonian name, Vistrítsa (Bistrítsa), the Aliákmon, throughout history, has served as a natural line of defense against invaders from the north, most recently in 1941 during World War II, when a New Zealand brigade was able to hold it briefly against the German forces invading Greece.