The Thermaikos Gulf is an enclosed coastal basin and constitutes the far north-western section of the Aegean Sea, in the Eastern Mediterranean. The city of Thessaloniki is located on its northern coast (40°64'N 22°9'E), and three rivers flow into the northern gulf along its western coast. The bottom relief in the region is generally mild, ranging from 30m in the north, to approximately 130m in the south at the shelf break, where the Thermaikos Gulf borders, through a sharp submarine escarpment, with the deep waters of the Sporades Basin. The region is characterised by weak tides and strong seasonal cycles of heating, wind forcing and freshwater input.
Various socioeconomic activities take place in the area, forcing the marine environment with residues from urban, industrial, agricultural and aquicultural activities. The gulf receives wastewater in the form of sewage outflows from the city of Thessaloniki (population 1.200.000) at the north-east (NE) area, where the major underwater pipe from the wastewater treatment plant discharges. It must be noted, that wastewater treatment started in the year 2001 and was fully functional, accepting the total of the city’s wastewater by the year 2003.