The prefecture of Thessaloniki, the largest of Macedonia, characterized by the presence of major waterways and low-lying areas. Out of the 3,560 square kilometres of the prefecture, 2,267 square kilometres of are lowlands, 612 sq.km
. is mountainous and 682 sq.km
. semi-mountainous, while the western part of the prefecture occupies the fertile plain of Thessaloniki, which leak rivers Axios, Loudias and Gallikos. The largest river crossing Macedonia and the second largest in the Balkans (after Evros) is the Axios or Vardaris, which has its source at the border between Albania and Macedonia, on Mount Sar (ancient Skardos). The authority has BA address, in the mountains between Suva, Gora and Bisora. Then crosses the valley of the Upper Axios, turns to pass through the stepa Derven, ushered in another kleisoura bottleneck in Taor and slowly emerges in the basin Gevgelis. It has a total length of 380 km, while the catchment area covers an area of 23,747 square kilometres.
The Greek part of Axios has a length of 76 kilometers and the catchment area around 2,300 square kilometres. It flows SSE , entering Greece from the prefecture of Kilkis and leaking a portion of the Plain of Thessaloniki. As flows between Axioupoli and Polykastro, continues south to the region Evropou and passing through the municipality Koufalion leaks in the Thermaic Gulf, opposite the Cape Mega Emvolo (Big Karampournoy), forming a vast delta, about 20 kilometers south of the city of Thessaloniki. West Valley Axios is the Paiko, with a peak around 1600 meters, which is one of the best places to observe the flow of the river from high above. The width of Axios varies greatly: in some areas it does not exceed 50 metres while in others it reaches 600 meters, while the depth can reach 4 m. The average annual rainfall in the region is estimated at 670 millimetres and the average annual volume