Results from both field measurements and laboratory simulation are used to assess the effects of disolved organic materials on turbid-water optical properties. Upwelled reflectance, attenuation, absorption, and backscatter spectral properties at wavelengths from 450 to 800 nm are examined in relation to water chemistry. From these data it is clear that dissolved organic materials decrease upwelled reflectance from turbid waters. Depending on wavelength, the decrease in reflectance is a nonlinear function of concentration with largest gradients at low carbon concentrations. Large increases in absorption coefficient (particularly at blue wavelengths) are observed with increases in dissolved organic material. Changes in backscatter coefficient are moderate, indicating minimal changes in particle scattering. Up-welled reflectance is highly correlated with two backscatter-absorption parameters used in certain optical models. Both backscatter-absorption parameters prove to be nonlinear with dissolved organic material concentration change.