Fifteen popular beaches and bathing spots are at risk of being shut for swimmers for an entire summer because of pollution fears.
Despite only four bathing areas failing to meet the minimum standards last year, the environmental watchdog has warned that figure could more than treble under European toughened regulations.
Out of 135 bathing spots checked in 2013, only Clifden in Galway, Lilliput on Lough Ennell in Co Westmeath, Dugort on Achill and Ballyloughane in Galway city failed to hit the mark.
But the Environmental Protection Agency (EPA) has named 15 swimming spots and beaches where notices might have to be posted warning of EU closure orders.
They include the Front Strand and Claycastle in Youghal, and Fountainstown in Co Cork; in Dublin, Sandymount Strand, Balbriggan Front Strand, Loughshinny, and the South Beach in Rush; in Galway, Ballyloughane and Grattan Road beaches and Clifden, Tra na bhForbacha, and Tra na mBan, An Spideal; Ardmore beach in Waterford; Lilliput in Westmeath; and Duncannon in Wexford.
But Peter Webster, EPA senior scientific officer, said beaches and popular bathing spots will not be policed to stop swimmers.
"The waters will have signage telling the public that the water classification was poor and advising against bathing," he said.
"But you can't stop people swimming, so people will be advised to check with the current status."
The tougher EU standards will use an average of water quality over the previous four years to determine if signs must be erected for the June-September season saying water may not be safe. The EPA is advising swimmers to use its splash.epa.ie site to see the most recent reports on water quality.
Despite the fears for the 15 swimming spots, Ireland does have some of the cleanest beaches in northern Europe.
Dr Matthew Crowe, director of the EPA's environmental assessment office, said there had been a sea change in quality thanks to better weather last summer.
"Irish bathing waters continue to be among the best in northern Europe," he said.
"By contrast to the 2012 bathing season, the warm dry conditions last year meant that many waters returned to their normal good quality."
The EPA warned that Clifden, which has had long-running problems with water quality, is unlikely to see significant improvements in water quality ahead of this year's bathing season despite planned remedial works on the waste treatment plant.
Lilliput was hit hard by a lengthy period of contamination late in the bathing season last August and September. It is thought to have come from a waste water source.
Dugort was affected by a rare pumping station malfunction, while the EPA said Ballyloughane suffered two pollution events, both linked to heavy rainfall.
The EPA study showed a very high standard of water around Ireland's 135 bathing spots.
Some 114 of Ireland's bathing spots are classified as good by the EPA.
It is assessing another 32 bathing spots to be included in the national list.