MODIFIED: An attempt to create a spa in a car has brought four Oamaru men to the attention of the police.

An attempt at a back seat spa has landed four young Oamaru men in hot water with the police.

The men, aged in their early 20s and late teens, were pulled over in their modified vehicle while driving down the main street on Sunday afternoon. The car had been modified to a convertible and a tarpaulin installed to hold the water.

Acting Sergeant Howard Jackson, of the Oamaru police, said the vehicle was pink-stickered and ordered off the road.

The driver was prosecuted for the vehicle not being up to warrant of fitness standard, alterations to the vehicle not being certified, and breaching a driver's licence. The passengers were also prosecuted for restraint offences.

"I've certainly not seen one like this in my 19 years of policing," Mr Jackson said.

"The lads were polite and accepted it was a silly thing to do, but just did it for a laugh and the owner plans to scrap the vehicle."