As a first step in optical modeling of coastal areas the effects of various suspensoids on optical parameters were studied in the Patuxent River, a subestuary of Chesapeake Bay. Particle populations were measured using a Coulter Counter, while both inherent and apparent optical properties were being monitored. Results are presented indicating strong relationships between beam attenuance and total suspensoids, including both suspended sediments (particle diameters between 1 and 5 x10-5 m) and phytoplankton (particle diame-ters between 15 and 35 x10-6 m). Relationships of natural phenomena such as tidal currents and daylight period with sediment and plankton populations are also demonstrated. As expected, efforts at predicting inherent optical properties from apparent, and vice versa, were not too successful. From these studies it appears possible to develop models capable of predicting, within reasonable limits, optical properties of coastal waters when local conditions such as weather, input stream characteristics, and local topographic conditions are known.