This paper describes the seasonal behavior of the water masses which occur inside the South Brazilian Bight, specifically inside the Santa Catarina Center-North Inner shelf. It is located between the Itapocu river and the Tijucas Bay. Inside the area there is the Marine Reserve of Arvoredo and the Itajaí river, the most important river of the State that reachs the Atlantic Ocean. Four surveys cruises was done since November 94 to July 95 making STD measurements. Wind data was obtained at an oil platform located 100 nautical miles off Itajaí city. During spring and summer the water columns was stratified and upwelling and doweling events occur according to the northern and southern winds. During autumn-winter period the water column was homogeneous because of doweling or advection of modified subantartic water trough the area.