This report provides the results of the first quantitative survey of the coral reef communities in the vicinity of the Mokapu Ocean Outfall in Kailua Bay, Oahu, Hawaii. This survey, conducted in April and July 1998, focuses on benthic and fish community structure and is designed to detect community changes that may be mediated by the release of treated sewage through the outfall. The Kailua Regional Wastewater Treatment Plant (WWTP), which has been operational since 1977, releases a little more than 13 mgd of secondary treated sewage through a 1.55-km-long discharge pipe at a depth of 32 m. If impacts are occurring to marine communities from a point-source discharge, their effects will be most evident in proximity to the source and less obvious with distance from the source. The sampling strategy used in this study focuses on quantifying the degree of development of marine communities adjacent to and at distances from the discharge source. This strategy should allow delineation of impacts if they are occurring. The results of this first survey indicate that the marine communities in the study area are diverse, with well-developed fish and coral components. This is particularly evident on the Mokapu Ocean Outfall diffuser (Transect T-1) where a high-biomass, diverse fish community occurs. This well-developed fish community is related to the shelter created by the diffuser pipe and basalt armor rock, as well as to the release of organic particles in the treated effluent which serve as a food resource for some fish species. The development of corals as measured in terms of live coverage in the diffuser pipe community is about half that found at the more distant sampling sites. However, a second sampling site (Transect T-2) located parallel to and 15 m away from the diffuser has coral coverage very similar to that found elsewhere in Kailua Bay. These data suggest that if the operation of the Kailua Regional WWTP is having an impact on marine communities, it is very limited in scope and scale.