The Caribbean Sea is an area that traditionally has been considered oligotrophic, even though the Orinoco River contributes large quantities of fresh water, nutrients, and other dissolved materials to this region during the wet boreal (fall) season. Little is known about the impact of this seasonal river plume, which extends from Venezuela to Puerto Rico shortly after maximum discharge. Here we present results from a study of the bio-optical characteristics of the Orinoco River plume during the rainy season. The objective was to determine whether the coastal zone color scanner (CZCS) and the follow-on sea-viewing wide-field-of-view sensor (SeaWiFS) satellite instrument can be used to assess the concentrations of substances in large river plumes. Recent in situ shipboard measurements were compared to values from representative historical CZCS images using established bio-optical models. Our goal was to deconvolve the signatures of colored dissolved organic carbon and phytoplankton pigments within satellite images of the Orinoco River plume. We conclude that the models may be used for case II waters and that as much as 50% of the remotely sensed chlorophyll biomass within the plume is an artifact due to the presence of dissolved organic carbon. Dissolved organic carbon originates from a number of sources including decay of dead organisms, humic materials from the soil, and gelbstoff. ¿ American Geophysical Union 1994