We tested for near-shore iron (Fe)-limitation of phytoplankton at the strong upwelling center at 30°S in the Humboldt Current System (Lengua de Vaca Point). Fe-amended and control microcosms showed differences in variable fluorescence consistent with Fe-limitation (dark-adapted PSII maximum quantum efficiency, functional absorption cross-section of PSII, and the time constant for quinone Q<inf>A</inf> oxidation). Evidence for Fe-limitation was strongest at a site within 4 km from shore south of Lengua de Vaca Point, where warmer, low chlorophyll waters came onshore due to upwelling relaxation and mesoscale circulation, and weak at a site north of Lengua de Vaca Point with higher initial chlorophyll. Alleviation of Fe-limitation in waters increased chlorophyll and particulate organic nitrogen (PON) but did not significantly affect particulate organic carbon (POC) or opal. Fe-addition at another nearshore site increased opal, but not chlorophyll, PON, or POC. The diatom Pseudo-nitzschia sp., a potential producer of the neurotoxin domoic acid, increased upon Fe addition. Fe-stimulated domoic acid correlated with alleviation of Fe-limitation indicated by variable fluorescence. Variation in Fe supply might be important to other trophic levels in the neritic system as scallop larvae consumed Fe-stimulated phytoplankton from the site showing Fe-limitation. Results confirm Fe-limitation of primary production can occur in very nearshore waters in the Humboldt Current System where the continental shelf is exceptionally narrow. Besides stimulating phytoplankton, inputs of Fe might increase phytoplankton toxicity, affecting other trophic levels. Even neritic ecosystems in this region may be sensitive to alteration of Fe input whether due to global or local changes.