We studied the reflectance spectra of the aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer. The three aquatic types-submerged, floating, and emergent-exhibited clear differences in their spectral reflectance and can be distinguished on the basis of discriminant analysis using reflectance parameters. This technique can be used in large-area mapping of aquatic plants. The normalized difference vegetation index (NDVI) and the simple ratio (SR) were well correlated with chlorophyll content, photosynthetic efficiency, and biomass in the emergent species. New, narrow-bandwidth indices and reflectance indices calculated from first and second derivative spectra were strongly correlated with the ratio of secondary and protective pigments to chlorophyll a and with epoxidation state of the xanthophyll cycle pigments, and therefore, with photosynthetic efficiency. These new indices may be useful in the remote sensing of plant physiological status.