Data are presented on hydrography, nutrients, phytoplankton standing crop and primary production in the Patuxent estuary (Maryland). Measurements of sedimentary carbon, nitrogen and phosphorus were compared with measurements of these elements in the water column. Nutrient levels were also measured. The effect of the Chalk Point Power Plant on phytoplankton primary production was studied. The data suggest that although the augmentation pumping system reduces the temperature encountered by the phytoplankton in the effluent canal, residual chlorine from the water passing through the condensers reduces production of all the water in the effluent canal to a greater extent than would be expected from simple mixing of condenser water with augmentation water. (Author)