The overheating warning symbol starts to flash in the upper middle of the LCD when the electronics reaches a temperature above 85°C/185°F.

If the camera becomes even warmer it will switch of automatically. The best way to cool it down is just to leave it shut off for an hour or so. Submerging a hot camera in cold water is not recommended because when the hot air inside the camera cools down an under pressure will occur that will challenge the water proof sealings.