During May and June, 1972, Department biologists made an ecological investigation in the vicinity of the discharge from Orange County Sanitation District off the mouth of the Santa Ana River. The survey consisted of 30 random benthic grab stations positioned within one mile of the discharge site, 8 bottom trawls, and underwater observations of the new and old discharge pipes.Abundance of polychaete worms in the grab samples indicates an area of enrichment adjacent to the diffuser in a northwest direction from the outfall.Trawl data show fish species composition and abundance comparable to previous monitoring surveys except for a high density at one station about one mile northwest of the outfall.Diving observations revealed normal biotic assemblages for this section of coast, however, previously noted growths of gorgonian corals at one station area were found in reduced numbers. (58pp.)