It is unclear how predicted rises in ambient temperature associated with climate change will impact upon the survivorship of oviparous reptiles. Given that the incubation temperature can influence hatchling phenotype, understanding how elevated temperatures during development can affect the ability of hatchlings to undertake routine behaviours is important, especially for threatened species. Here we tested if raising mean incubation temperature above natural levels altered the physiology of hatchlings to an extent that behavioural function was impaired. Firstly, incubation temperatures were recorded from nests of the freshwater turtle (Elusor macrurus) in the wild, and the observed thermal range (26–31 °C) used to define the experimental protocol. Then, freshly laid E. macrurus eggs were collected and incubated at three constant temperatures (26, 29 and 32 °C). Embryos incubated at 32 °C had the lowest hatching success. Those that did hatch were smaller than the other groups and had a reduced post-hatch growth rate. On land, the ability of hatchling turtles to right themselves is critical, and the turtles incubated at 32 °C took 30-times longer to do this than those incubated at 26 °C. Once in the water, hatchling turtles must be able to swim effectively to evade predation and obtain food items. During swimming trials the 32 °C group exhibited a lower mean stroke force (10.5±0.3 mN) and spent less time swimming (133.7±17.7 s) compared with hatchlings incubated at 29 °C (13.4±0.4 mN, 281.3±25.7 s) and 26 °C (15.7±0.5 mN, 270.8±28.5 s). The results of the present study illustrate that even slight rises in the mean incubation temperature, over that observed in the wild, can impact upon a hatchling's performance.