The effects of the addition of sediments on the upwelling radiance from pure algal cultures is examined. Upwelling reflectance signatures for both algae and suspended sediments are determined by the reflectance of the particles themselves, as well as absorbance by the water surrounding the particles. The addition of sediments to pure cultures of algae increased the reflectance at wavelengths longer than 550 nm. This effect was equal for wavelengths longer than 600 nm and subtraction of reflectance at 660–720 nm is suggested as a means of compensating for these effects.