The rows of boats parked on Swansea prom at Mumbles are familiar to the thousands who walk past them every month.
But according to a report to Swansea Council, some of the owners haven't paid fees to the local authority for a decade.
Spot checks of boats kept out of the water at Knab Rock, Village Lane, and Southend revealed the discrepancy, the council's audit committee was told.
The report before the committee said the spot checks unearthed a significant number of unknown boat owners, and also owners who were known but hadn't paid for years.
It said the Village Lane site had boat parking arrears going back the furthest - about 10 years.
The report said previous audits had identified the unknown owner issue, but no action had been taken.
Cultural services manager Jamie Rewbridge said the responsibility for managing boat parking was being moved from his section to another council department at the time of the audit.
He said boat storage in Mumbles was a historic issue because of the open character of the sites, and that there had been issues in the past with the council removing illegally parked boats and then being challenged for costs by the owners.
Councillor Mike White asked if the council had a means of knowing who all of the boat owners were, and what the legal position was in terms of clawing money back.
The huge queues in Mumbles' new M&S store:
"If this was somebody's private business, they would probably have gone bust by now," he said.
Mr Rewbridge said a database had now been set up with this purpose in mind, that photos had been taken of all of the boats at the Mumbles sites, and notices had been placed there requesting owners to get in touch - or potentially face having their craft auctioned or disposed of after three months.
He added that 45 invoices - some backdated - had been raised this month totalling £6,000, but it was expected that some owners might query them.
