Genistein and daidzein are two estrogenic compounds derived from plants, especially legumes. This research begins to explore their environmental fate, focusing on direct and indirect photolysis. UV-visible spectra for both compounds at varying pH values were taken, the pK(a) values for both compounds were measured, and UV-visible spectra for each protonation state were determined. The loss of both compounds in deionized water was observed upon exposure to natural sunlight, and the quantum yields were determined for each protonation state. In Mississippi River water, direct photolysis does not account for all of the loss of genistein and daidzein. The mechanism of indirect photolysis was probed using quenchers and sensitizers, and results suggest that daidzein is transformed mainly via direct photolysis and singlet oxygenation, while genistein is transformed mainly via reaction with triplet-state natural organic matter. The parameters determined in this study will allow for estimation of the concentration of genistein and daidzein in sunlit surface waters, which will allow for assessment of any risks posed to aquatic wildlife.