A simple theory is developed relating Secchi disc depth to reflectivity, just below the surface, in the green band. The theory contains one adjustable constant, B, the ratio of backscattering to total scattering coefficients for suspended particles. A method is then outlined for correcting the satellite data for atmospheric effects. Secchi depths are then compared with reflectivities, in the green, in two Landsat Multi-spectral Scanner (MSS) scenes. It is found that for Secchi depths< 16m, the theory provides a good fit to the data with B = 0.0077.