The region of fluvial influence (ROFI) of Itajaí-Açu River was assessed through fourteen surveys covering thirty sampling stations in a radial shape with origin in the estuarine inlet. The total sampled area was of 100 km2 , with depth ranging from 6 to 25 m, and until 10 Km offshore. The surveys were nearly monthly, from October 2002 to December 2003. The variables collected were salinity, temperature, suspended particulate matter, dissolved oxygen, chlorophyll a, picoplankton (autothrophic and heterothrophic) and zooplankton. River discharge and meteorological data were also obtained to help in the general characterization. The results indicated that in terms of averaged values of each variable, the sampling area is poorly related with the river discharge, or in other words, the sampling area is wider than the ROFI. Only salinity showed reasonably agreement with river discharge, although during the winter the region is affected by the Plata estuarine front. Further analysis on the data gathered must cope with spatial variability, either horizontal, e.g., plume dispersion, as vertical, e.g., plume buoyancy flow.