A reader contacted the Otago Daily Times with a picture showing the rocks, which had been used to prevent cars from parking in Tunnel Beach Rd, had been removed.
The reader assumed they might have been moved by someone annoyed a previously used parking area had been blocked.
A council spokeswoman said staff were made aware of the incident, in which two rocks had been dislodged and rolled downhill and another had been nudged to its side, on Friday.
"We have no idea who did this," the spokeswoman said.
"We will work with contractors to put the rocks back in place, but it might be a few days before it happens."
The rocks had been placed to manage the site and were part of the resource consent conditions.
"It’s extremely disappointing that someone has chosen to do this.
"It’s not the best way for the contractors to spend their summer break."
The closest carpark to Tunnel Beach is open every day from 8am to 9pm, from September to March, and from 9am to 5pm from April to August.
The spokeswoman said the carpark was closed at night because one of the resource consent conditions for the site was no freedom camping was permitted there.
Earlier this year, the ODT reported dozens of residents were annoyed with these moves, as they liked to use the spot at night for astro-photography or other activities
A Tunnel Beach Rd resident had informed the council about the incident, but the council was still no closer to finding out who moved the rocks, or what the cost would be.
"In the meantime, we would like people to park in the designated areas," the spokeswoman said.
