Lusty couple Elissa Alvarez, 20, and Jose Caballero, 39, found themselves on the wrong side of the law after their romp in the sand was caught on film.
The pair cavorted for more than 25 minutes before wandering off for a swim.
When they started up again a disgusted grandma filmed their actions on her mobile phone before calling police.
Officers arrived and arrested the couple – on the beach in Florida and charged them with lewd behaviour.
They added that one of the witnesses was a 4-year-old girl.
The woman who recorded Alvarez straddling Caballero on a blanket said: “This went on for about 25 minutes.
“I’ve lived here since 1978 and I go to the beaches, and I’ve never seen anything like this.”
It was reported that although people who noticed what was going on were appalled, no one called police at first.
The Florida couple apparently then went for a swim before returning to their blanket for a snooze.
The witness said: “They laid on the beach and passed out for hours. We thought they were dead. But when they woke up, they cuddled for a while – then they started into the same thing they did before.”
This time, though, the horrified mum of the four-year-old girl called police.
Caballero – a personal trainer who was released from jail last year after an eight-year stretch for cocaine trafficking – and Alvarez were nabbed by officers in the city of Bradenton.
Police said the pair have been charged with lewd and lascivious exhibition, and they have been ordered to appear in court in August.