Contamination of the aquatic environment by EDCs has received considerable attention from scientists, government officials, and the public. E2, one of the EDCs with high estrogenic effect, has the potential to cause multiple endocrine-disrupting effects, even at small concentrations. In the present review, the toxicity of E2 to aquatic organisms was reviewed. Results of published studies show that, for aquatic species, reproductive effects were the most sensitive endpoint for E2 exposure.Although the risks posed by EDCs have caused much attention, the research on the WQC 'for EDCs is still at the initial stage. It has been suggested in several reports that the PNEC can be regarded as the most appropriate reference value for developing WQC for the EDCs. The SSD method was applied to derive PNECs that were based on reproductive effects endpoints. In the present review, 31 NOECs, based on reproductive effect endpoints for different species, were selected to construct the curve. ThePNEC value was determined to be 0.73 ng E2/L, which could protect the biodiversity of aquatic ecosystems. Moreover, 6 NOECs for multigeneration species were also analyzed in anticipation of sensitivity comparison between the Fa and the F1 generations.When multiple generations of aquatic species were exposed to concentrations no greater than 100 ng E2/L, nearly 71.4% of the F 1 generation individuals were more sensitive to the effects of E2 than those of the Fa generation. This result indicated that different generations of the same species may respond differently to EDCs exposure.Individuals of the F 1 generation were slightly more sensitive than those of the Fa generation,in general. Therefore, protecting the F1 generation of aquatic organisms is particularly important when WQC values for the EDCs are established.Considering the toxic effects of EDCs on reproduction, long-term toxic effects(viz., full-life cycle study and the most sensitive life stage) should be used in settingWQC. Unfortunately, the NOECs of E2 for multigeneration species did not meet the requirement of PNEC derivation for protecting the Fl generation. Therefore, further research results are needed on the Fl generation of aquatic species to provide more insight into what constitutes adequate protection for aquatics lives. In the present review, the PNEC values derived in the study were compared to thePNEC values developed by others, and the results showed that they were highly consistent. In addition, we also compared the PNEC value for E2 to the PNEC value for EE2, a similar estrogen, and the result was also highly consistent when their EEFs were considered. These comparisons affirmed that the method we used for deriving the PNEC value of E2 was reasonable and the PNEC values we derived were acceptable for protecting aquatic organisms. By comparing the PNEC values we calculated to actual E2 concentrations in the natural water environment, we found that E2 in surface waters may pose high risks in many countries, especially China, Japan, the USA, Great Britain, and Italy.