They were among 5,000 people due to take part in a swim in the River Seine, but it was cancelled amid fears about the water quality.
Instead, Matt Newbury, La La Mahakama and Queenie Martin chose the Trocadero Fountains as a substitute.
Dressed in union jack swimming caps, the trio's "impromptu water ballet" amused hundreds of spectators.
"We were gutted when the Seine swim was cancelled at short notice - the authorities in Paris said they were worried about the water quality," Mr Newbury said.
"We decided we'd go ahead and I came up with the idea of the Trocadero Fountains in front of the Eiffel Tower.
Mr Newbury, a 42-year-old press officer from Torquay, said having taken the decision, the trio "staked out" the venue before taking the plunge.
"We obviously didn't ask permission, so I guess you could say we were urban guerrillas," he said.
Mr Newbury, who describes wild swimming as "anywhere that isn't a swimming pool", said the fountain swim had been a wonderful experience.
He is a member of the Devon and Cornwall Wild Swimming Association - a network of swimmers who enjoy swimming outdoors in rivers, waterfalls, caves, lakes and the sea.
The video evidence of the swim in Paris was filmed and edited by Mr Newbury's partner Aaron Kitts.
Three Devon wild swimmers say they have become "urban guerrillas" - by swimming near Paris's Eiffel Tower.