Some previous studies indicate that the local hydric environment may influence sex determination in turtles with temperature-dependent sex determination. In this study, the effect of a daily application of 0.77mL of ddH20 per egg using an incubation temperature of 29.1°C was examined during the temperature-sensitive period for two consecutive nesting seasons. This regimen yielded sex ratios of 11.8 and 11.1% male in control groups not receiving water supplementation, whereas daily water treatments resulted in sex ratios of 86.7 and 45.7% male during the 2006 and 2007 nesting seasons, respectively. The results indicate that daily water treatments significantly influenced sex ratios (P<0.001). In addition to providing insight on the physiology of sex determination, these results could have implications for studies predicting sex ratios from nests on natural nesting beaches that are periodically exposed to rain. © 2008 Wiley-Liss, Inc.