ABSTRACT Field studies have established the concentrations of naphthalenes in bay sediments and water in the vicinity of a shallow-water@ oil-separator platform and their effects on the benthic fauna. Fifteen stations were occupied each month@ from July 1974@ to December 1975@ along three transects extending from the separator platform outfall outward for a distance of 2.5 to 3.5 miles. A lesser number of stations were occupied from April 1974 to June 1974. Bottom sediments at each station were analyzed for total naphthlenes concentration and for numbers of species and individuals. All stations were located in six to nine feet of water. The outfall was located three feet off the bat bottom. There was a definite inverse correlation between sediment naphthalenes concentration and numbers of species and individuals. As expected@ the first station@ located 50 feet from the outfall@ had the highest concentration of naphthalenes of all stations sampled. The levels of naphthalenes dropped sharply from the outfall station to the stations located 250 feet from the platform@ the later containing about 20-50% of the levels found 50 feet from the outfall. Concentrations of naphthalenes decreased gradually to near background levels at stations farther out. Hydrocarbon concentrations in bottom water 50 feet from the outfall were three orders of magnitude lower than those in the full-strength effluent@ but sediments 50 feet from the outfall had hydrocarbon concentrations four times as great as in the full-strength effluent.