Gene Cernan, Apollo 17 commander, crashed a Bell 47 helo into the Indian River in 1971 while showing off for some boaters. Smooth water was cited as a cause in the accident report:
On October 18, 1971, a NASA press release stated that “misjudgment in estimating altitude” was the primary cause of the crash. The board listed possible mitigating factors which may have contributed to Cernan's failure to realize that he was flying into the water. These included a lack of familiar objects on the river surface to help him judge altitude, possible visual focusing on a false water surface because of the water's millpond smoothness and a change in sun reflection on the water cause by the change in course just prior to the accident.
The board also conjectured that Cernan's extensive experience with high-speed aircraft may have contributed to his altitude misjudgment. The thought goes: the lower a pilot flies in a jet aircraft, the faster the surface appears to pass by. The effect is not as pronounced in a slower aircraft such as a helicopter.
The crash almost caused Captain Cernan to lose his place in history as the "Last Man on the Moon":
James McDivitt, an Apollo Manager at the time, demanded that Cernan be removed from flight status and not be given command of Apollo 17, as the master Apollo manning plan called for. However, Cernan was defended by the chief astronaut, Deke Slayton, and given the Apollo 17 command. Upset by the decision, McDivitt resigned as an Apollo Manager shortly after the Apollo 16 mission in June of 1972.
Gene Cernan went to the moon on the final mission of the lunar Apollo program. Cernan became "the last man on the moon" since he was the last to re-enter the Apollo Lunar Module during its third and final extra-vehicular activity (EVA).
Regarding his 1971 helicopter accident: in later accounts, one of which was written by Cernan himself in an autobiography, it is revealed that Cernan was flying too low and showing off for nearby boaters. Cernan often describes the experience as "Mr. Toad's Wild Ride."
Cernan's '71 Helo Crash