Water masses characteristics of the northern Aegean Sea were investigated based upon historical Nansen cast data. Cyclonic surface circulation carries Black Sea water towards the west, and it then follows a south-south-westerly route. Less saline surface water of the Black Sea origin was observed in the western part of the area. The source of intermediate water was identified by slightly elevated salinity located in the south and south-eastern parts of the region. Intermediate water transport towards the north and north-west may possibly compensate for south-bound surface water transport. Deep water with high oxygen content is formed in the Kavala, Kassandra and Saros Gulfs of the northern basin.