Reports that a swimmer was in trouble next to the River Gardens in Belper caused the police helicopter to be scrambled.
A 999 caller told operators they had spotted someone waving their arm in the water on the other side of the River Derwent.
A chopper and two police cars raced to the scene at around 11.30am on Friday, January 4. However, after a search they were unable to find anyone in difficulty.
A spokesperson for Derbyshire Police said: “It appears it was a false alarm. The man simply had his arm in the air.”