The variability of the MODIS chlorophyll concentration in the northern Adriatic Sea is described between July 2002 and January 2005 and related to the Po River discharge rates and local wind forcing. After interpolation, the MODIS data were decomposed into EOF modes. Significant variability (~61%) is explained by the first three modes in which mode 1 includes a strong seasonal cycle with enhanced signal in winter for the open sea waters and a second maximum in April--May, and mode 2 separates the coastal and river-influenced waters, from the open sea area. The temporal amplitude of the modes is significantly correlated with the Po River runoff. The interpolated MODIS data were also correlated with the Po River discharge rates, resulting in significant positive correlation north and south of the delta and off the Croatian Islands. When correlated with wind speed, the MODIS chlorophyll shows positive correlation in the area off Istria, off Croatia and at the edge of the coastal layer north of Ancona. Using wind regimes, similar patterns are found for the Bora-wind like winds. In contrast, for Sirocco-like winds, the correlation is significantly positive in the vicinity and north of the Po River delta. The regions off Ancona and Istria have poor correlation with the Po and wind because the MODIS chlorophyll variability is associated with mesoscale instability features not directly related to these forcing parameters. Poor (and even slightly negative) correlations are found off the Po delta. In most areas, correlations reach maximum values after 1--2 days.