Vandals managed to open the gates at Newcastle Ocean Baths early on Thursday morning and let thousands of litres of water back into the ocean.

Newcastle council staff arrived at 4am to fix the problem and by 9am swimmers were making the most of the water that was there to cool off.

It is unclear how the vandals opened the gates, a council spokeswoman said.

The situation forced some swimmers to go to Merewether Baths to cool off.

They were caught off guard when it closed for cleaning at 11am.

Some thought the council should have rescheduled the clean, saying the 39-degree heat made the situation inconvenient.

Novocastrian Brian Stevens was among the swimmers who arrived at the baths as it closed.

He said it was “annoying” and “an inconvenience” on a hot day, but admitted he had not checked the cleaning schedule, which was released earlier this year. 

“It’s good to come here to cool down,” he said.

A council spokeswoman defended the decision, saying staff waited until the Newcastle Ocean Baths had been refilled before they closed Merewether for cleaning. 

She said changing the schedule would inconvenience more swimmers.

“Users rely on the timetable to plan their visits,” she said. 

“More people get more frustrated with us if we chop and change the schedule.

“The cleaning schedule is from July to December [and released before the start of the financial year] so people have plenty of time to look at it.

“There’s also signage at the beach that shows when it will be cleaned.”

The baths are cleaned each week during low tide so the water can be released into the ocean.

It takes about 1.5 hours to empty it and four hours to refill.

Merewether and Newcastle baths are cleaned at different times so residents can take a dip at one of the sites.

Merewether Baths re-opened to the public in November last year after a $4 million upgrade that transformed the iconic site.