Axios or Vardaris is the longest river that runs through Macedonia and second largest in the Balkans (after River Evros), with a length of 380 km, of which only the 76 are on Greek territory. Its width ranges from 50-600 m. and its depth reaches 4 m. It spurs from the Mount Skardos (Sar), in the Serbian-Albanian borders, it crosses the valley of FYROM, comes to Greek territory, crosses Macedonia and pours into Thermaikos Gulf. In the area that Axios flows, a delta is formed; an area of 22.000 acres. In this region, the Rivers Loudias, Aliakmonas and Gallikos are also flowing and along with the salt marshes of Kitrous, they create a large wetland of great extent and importance, which is protected by the Ramsar and Berne Convention. The "evryrreon" river of Homer enters the Greek land having traveled three hundred kilometers from its source in the Serbian-Albanian Šar Mountains, without a passport, waters valleys and fields, nourishes the soil, giving life, sweetening the atmosphere, and leaking the land of ancient Paeonia it pours into the arms of Thermaikos Gulf.
A river known since the ancient times, it was praised by Homer in the Iliad as "kalliston water" and Euripides in "The Bacchae" calls it "okyroan". The river, which takes its name from the mythical Axios, ancestor of Paionian Kings, offers with a ruler’s magnificence its riches in its path through the centuries. From its source to the mouth, it hosted celebrated cities such as Ichnes, Europos, Amydona and Pella.
During the medieval times, in the works of Byzantine writers it is presented with the name Vardaris, which is derived from the verb varvarizo {making noise}, or the exclamation varda, which means beware or the Persian word "Bahr-Dar" meaning great river. The northern wind that comes from the direction of Axios, the wind of Axios, is also named Vardaris.
Axios supports an important number of species of fauna and flora, and for this reason it is considered throughout its length as a special interest habitat of particular importance, also due to the delta of Thermaikos that is protected by the International Convention of Ramsar. Plane trees, alders, willows and poplars, cormorants, ducks and herons, tree frogs, squirrels and coypu, carp, perch and eels are the daily companions of the river.
It has been included in the NATURA 2000 network, code GR 1220007.