We exposed a native endangered species, bonytail chub (Gila elegans), to graded concentrations of secondarily-treated effluent. At the end of each treatment period, we collected water from all raceways and samples were analyzed for the presence of 83 organic wastewater compounds. We extracted blood plasma from control and treatment fish in each raceway and samples were analyzed for hormones, 17β-estradiol and 11-ketotestosterone, and the egg yolk protein, vitellogenin.17β-estradiol concentrations were consistently lower in treatment females than those detected in control females. The 17β-estradiol and vitellogenin concentrations were always higher in treatment males than those found in control males. Concentrations of 11-ketotestosterone were consistently lower in treatment males than those detected in control males.Endocrine disrupting effects occurred in male and female fish exposed to low concentrations of effluent. Changes in hormone levels suggested a feminizing effect in treatment male fish and an androgenizing effect in treatment female fish.