Abstract: The southern California marine environment has been subjected to numerous inputs of pollution; however, little is known about pollution effects on infestation of parasites on fishes. Pollution exposures may result in stress, potentially decreasing the immune response in fishes and increasing their susceptibility to diseases and parasites. Alternatively, these conditions could decrease the host's susceptibility and/or otherwise adversely affect the parasites. A variety of marine organisms has been evaluated as potential biological indicators of pollution; however, due to the range of contaminants, contaminant concentrations, and exposure time that marine organisms experience, it is unclear which fishes and/or anomalies are relevant. During the Southern California Bight 2003 Regional Marine Monitoring Survey (Bight'03), selected marine fishes were collected by otter trawl from 79 stations adjacent to and away from four large wastewater outfalls and inspected for ectoparasites. This study evaluated the conditions around wastewater outfalls in terms of infestation of ectoparasites on fishes. Results suggest that specific parasite and/or host species, such as Holobomolochus prolixus on Citharichthys stigmaeus, and total parasitization on Hippoglossina stomata and Pleuronichthys verticalis, can be used as bioindicators of environmental stress in the Southern California Bight. Results show many parasites have high host specificity and have potentially coevolved with their fish hosts and thus have high attachment-site specificity. Parasite prevalence and intensity varied according to host species, which suggests that some host species may be more resistant to parasitization or have evolutionarily lost their parasites. In addition, the prevalence of Austrobdella sp. 1 on Scorpaena guttata was significantly higher at one Large-Outfall area compared to the other three sampled, indicating a narrow range of this parasite. Naobranchia scorpaenae on S. guttata had a high mean intensity at two distant areas, suggesting the use of ectoparasites as biomarkers and potentially resulting in some insight to the movement patterns of this host. Hosts examined totaled 15,848 individuals representing 34 species, and ectoparasites removed totaled 14,620 individuals, including monogeneans, leeches, branchiurans, copepods, and isopods. Three new species of leeches, one new species of parasitic copepod, and 56 new host records were found in this study.