Upwelling radiance from pure cultures and natural populations of freshwater algae is examined. The effects of changes in the vertical distribution of the algae on the upwelling radiance are also explored. The different algae studied were spectrally very similar. The volume reflectance for any given chlorophyll concentration differed between the Phyla studied. This appeared to be due to the colonial nature of some species. Higher chlorophyll concentrations resulted in higher reflectance in all but the blue wavelengths, and correlations between reflectance in the near-infrared andLnlorophyll were the highest. This suggests that remote sensing of algae in inland waters should be based on increased scattering by the cells and not increased absorbtion by chlorophyll.