The distribution and abundance of emerging Culex spp. were assessed within narrow (width: 3 m) and wide (width: 20 m) bands of California bulrush (Schoenoplectus californicus) and in the open water adjacent to emergent vegetation in 2 marshes of an ammonia-dominated wastewater treatment wetland in southern California. Emerging mosquitoes were collected along transects perpendicular to the path of water flow at 3 distances (1.5, 5, and 10 m) from the vegetation–open water interface in the wide bands of emergent vegetation, at the center of narrow bands of emergent vegetation, and at 1.5 m from the edge of emergent vegetation in the open water. The width of vegetation bands (3 vs. 20 m) influenced the effectiveness of integrated mosquito management practices, especially the application of mosquito control agents. Mosquito production from the 2 marshes also differed up to 14-fold, suggesting that the distance between the shorelines (62 vs. 74 m) of each marsh also influenced the efficacy of mosquito control agents applied from the shore and boats. Hot spots of mosquito production (75–424 female Culex/m²/day) were found within the wide bands of bulrush. During summer, the relative abundance of Culex stigmatosoma among emerging mosquitoes increased from the periphery to the center of wide bands of emergent vegetation. Culex erythrothorax emergence rates were comparatively similar among the transects in the wide bands of emergent vegetation. Culex tarsalis adults increased in number from the periphery to the center of wide bands of bulrush and, in May, were >95% of emerged mosquitoes.