Up to 10 nudists chased down a naked man on South Australia's Maslin Beach after he was spotted with a camera hidden inside his esky.

It was claimed the man, thought to be in his 40s or 50s and wearing only an Akubra hat, was seen positioning his esky to face other unclad people on the nudist section of the iconic beach.

A woman reportedly walked past and saw a wooden contraption inside his esky with a video camera set up to film though holes.

He was confronted by nudists, only to walk further down the beach and position his esky to face another naked couple.

A group of nudists then chased the man down the beach and made a citizens arrest until police arrived.

The incident happened on December 21 but police said there was insufficient evidence for a charge of indecent filming.

They examined the camera and found no vision had been recorded, but cautioned the man and asked him to leave the beach.

The southern section of Maslin Beach was declared Australia's first official nudist beach in 1975.

Pilwarren Maslin Beach Nude Games organiser Debbie Pillar is preparing to hold the annual event next month on the beach.

She told 891 ABC Adelaide she was not surprised that a group of nudists had chased down the man.

"All nudists are generally friendly people and they look out for each other," she said

"If they happen to see someone down there doing the wrong thing, they will basically go up to them and ask them kindly not to film or photograph without their permission.

"If they continue doing what they're doing, then your next resort is to contact police and get them to deal with the situation."

She said there was a misconception about nudism among some people.

"It's not us that are going around filming people," she said.

"It's the perverts, the undesirables, who are going out there making it uncomfortable for the people who genuinely want to enjoy the lifestyle."

Police warned members of the public to remain aware of their surroundings and continue to report any suspicious behaviour.

They said penalties for indecent filming could include a $10,000 fine or two years imprisonment.

Penalties are much higher for incidents involving children, including up to 12 years jail for aggravated offences.