Multiple environmental agencies have promulgated perfluorooctane sulfonate (PFOS) aquatic life criteria. In prior work, we noted a single threshold value (0.6 µg/L) for zebrafish (Dario rerio) exerts a strong influence on freshwater species protection levels developed by the Environmental Protection Authority of Victoria, Australia. The study from which the value was derived was limited in scope, featuring only 3 PFOS dose levels and 2 replicates per dose. The value led to a 99% protection level of 0.00023 µg/L, more than 1000X lower than criteria calculated by other regulatory agencies. Given the influence of this study, the US Army Corps of Engineers Environmental Research & Development Center and the Sediment Management Work Group partnered (with oversight by the US Environmental Protection Agency) to repeat the multiple generation PFOS evaluation with a more robust experimental design. Based on results with the parent generation (lethality, length, body mass, and egg production data measured up to 180 days post fertilization (dpf)), the strongest evidence of dose-dependent, potential ecologically significant effects was noted for the highest dose level (100 µg/L). This level indicated minor, but not statistically significant, 14% lethality (relative to controls) at 180 dpf and a statistically significant 21% effect on body mass at 60 dpf (but not 90 or 180 dpf). Minor (3-4%) statistically significant effects on length in male fish (but not female fish) were noted for the 20 and 100 µg/L dose levels, although this level of response does not reflect ecologically significant effects. Reproduction was unaffected at all exposure levels. Preliminary results indicate the threshold for ecologically significant effects is 100 µg/L or higher, and not 0.6 µg/L. The 99% species protection level calculated using the 100-µg/L value is 1.3 µg/L, as opposed to the current protection value of 0.00023 µg/L. Additional results will be forthcoming.