The main purpose of this paper is to explore seasonal variability of the local hydrography and investigate the water masses, their seasonal and regional variations in the vicinity of Izmir Bay based on data sets collected between 1994 and 2003. The general water movement characteristics in the bay are provided by CTD data analysis together with Killworth's general circulation model. In the bay, three distinct water masses exist: ASW ( Aegean Sea water), IBW (Izmir Bay water) and IBIW (Izmir Bay inner water). Generally, vertically homogenous ASW enters the bay from the north, near Karaburun in winter, and horizontally homogeneous ASW inflow occurs above a pcynocline through the Foca-Karaburun vertical section in summer. The outflow occurs in the sub-surface and bottom layer near the coast of Foca in winter while it flows out under the pycnocline in summer as a result of thermohaline behavior of stratified water. Wind-driven circulation causes cyclonic or anti-cyclonic movements in the middle section of Izmir Bay. Cyclonic movement takes place under the influence of southerly and westerly winds. On the other hand, northerly and easterly winds cause an anti-cyclonic movement.