Effects of granular formulations of chlorpyrifos, temephos, and diflubenzuron on nontarget invertebrates in 2 residential-recreational lakes were studied during June, 1976–Jan., 1977. Chlorpyrifos at 0.22 kg (.0074 ppm) AI/ha in partial areas (fingers) of one lake, and at 0.14 kg (.003 ppm) AI/ha in the other entire lake was evaluated. Temephos at 0.28 kg (.0092 ppm) AI/ha in the fingers, and at 0.17 kg (.0042 ppm) AI/ha in main areas of the same lake was tested. Diflubenzuron at 0.11 kg (.0037 ppm) and at 0.22 kg (.0074 ppm) AI/ha was applied to the fingers only.All 3 chemicals reduced populations ofDaphnia pulexLeydig andDaphnia galeataSars from the fingers but they recovered within 1–3 wk.Bosmina longirostris(O. F. Muller) was susceptible to temephos and chlorpyrifos but tolerated diflubenzuron.Cyclopssp. was affected by temephos only.Diaptomusspp. were affected by diflubenzuron, slightly at the lower and severely at the higher rate, recovering within 2 wk.Cyprinotussp., tolerant to temephos, was reduced by chlorpyrifos, 60–90% in the fingers, and up to 80% in the main lake, recovering in 1–4 wk.Cyprinotussp. also was affected by diflubenzuron at 0.22 kg AI/ha.Hyalella azteca(Saussure), tolerant to temephos, was markedly reduced by chlorpyrifos as well as diflubenzuron for several wk. Oligochaetes (mostly Naididae) were not affected by any treatment employed during this study. The impact on nontarget organisms was much more severe and longer lasting when most or the entire habitat was treated as compared to partial treatments in semi-isolated fingers.