Seston, particulate carbon, relative irradiance and Secchi disk depth measurements were taken at eight stations in the esturaine portion of the Patuxent River for two years. Seston values in the central portion of the estuary were high as a result of resuspension in the “sediment trap.” In this estuary, seston concentration cannot be precisely estimated from either Secchi disk depth or the attenuation coefficient of diffuse light. The attenuation coefficient of diffuse light (k) may be calculated from the equation:k=1.43 [Secchi disk depth (m)]−1.