This is the first record of immature stages of species belonging to the subgenus Nyssorhynchus (Blanchard) in eutrophized breeding habitats. Larvae of Anopheles (Nys.) evansae (Brethes), Anopheles (Nyssorhynchus) rangeli (Gabaldon et al), Culex nigripalpus (Theobald) and Culex quinquefasciatus (Say) (Diptera: Culicidae) were collected in a rural eutrophized dam in Rio de Janeiro State, in Southeastern Brazil. Eutrophication was substantiated by the low diversity of mosquitoes, the high incidence of Cx. quinquefasciatus (42%) and of Daphinia sp. and, the high levels of both organic nitrogen (0.28 mg/l) and total phosphorus (0.02 mg/l).