Dublin City Council has blamed bird droppings for the latest closure of Sandymount Strand.
The beach has been closed because of water contamination, which authorities are blaming on droppings from the large seagull population.
The frequent closure of the popular coastal spot to bathers since the start of summer has been slammed by Labour Cllr Dermot Lacey.
Sewage overspill caused by heavy rainfall was the cause of the two previous closures of the strand.
"This is a beach just yards from where hundreds of thousands people live," Cllr Lacey told the Herald. "It is an area that should be given massive attention to facilitate people, especially for those not going on holiday.
"I have called before for investment in the beach and it has never been given the priority it deserves.
"It's really, really disappointing. I was just down there a few days ago and I just thought how lovely it was, what a great place it was for people to go to."
Cllr Lacey said Dublin City Council needed to do more to ensure the water was not so easily affected.
"A private company is about to reopen the old Clontarf baths," he said.
"If a private company can do that, surely the city council can do something to provide a clean bathing area in the Sandymount Strand area."
A spokesperson for the Environmental Protection Agency (EPA) said the presence of a sandbar at one of Dublin's favourite swimming sites attracted "all kinds of seabirds and gulls", and that it was their droppings that was probably causing the contamination.
An EPA report issued in 2015 explained that the droppings of sea birds were particularly detrimental to water quality.
Meanwhile, there was further water chaos for bathers in Kilkee, Co Clare.
The area's beach, a massive tourist attraction for the region, was hit by a sewage overspill earlier this week.
Signs have been posted warning swimmers that bathing is prohibited because of the "risk of increased bacterial levels".