The Aliákmon (Greek: Αλιάκμων) is the longest river in Greece, with a total length of 322 km (200 miles). It rises in the mountains of northern Greece near Lake Prespa on the border with Albania and the Republic of Macedonia, before flowing southeast then northeast through the Greek provinces of West and Central Macedonia into the Thermaic Gulf . It waters an extensive area, making it of great importance to agriculture in the region. The river forms the western portion of the delta of the Axios.

Also known as the Vistrítsa River, in ancient times the Aliákmon was known as the Haliacmon.