Two thirds of Ireland's bathing areas are deemed to have "good" water quality, according to the latest report from the Environmental Protection Agency.
Only 91 of the 136 designated bathing areas met the EU standards in 2012.
This is lower than the 112 that met the standards for "good" water quality in 2011.
However, all but four of the 136 bathing areas (97.1%) were deemed to have "sufficient" water quality by meeting the basic EU mandatory standards.
The four that failed to comply with these minimum standards, and so are deemed to have "poor" water quality, were Clifden Beach in Galway, Fountainstown in Cork, Rush in Co Dublin and Ballyheigue in Kerry.
Of the 18 local authorities that have designated bathing areas, three achieved "good" water quality status for all of their identified bathing waters.
These were Dún Laoghaire-Rathdown, Sligo and Leitrim, however, these only account for 6% (eight of 136) of all bathing waters.
EPA Programme Manager Dr Micheal Lehane said bad weather was a factor in the drop in standards in some areas.
Speaking on RTÉ's News At One, Dr Lehane said there was intense rain last summer on already saturated ground, which lead to agricultural run-off and discharge from storm water overflows ending up in rivers, streams and bathing areas.
He said local authorities need to be vigilant about maintaining infrastructure and ensure that there are good agricultural practices in their area.
Dr Lehane said Clifden has failed in the past and needs an urban waste water treatment plant, which should help the problem.
He said the local authority for Rush believes its poor result was due to heavy local rainfall and possible problems with the pumping station nearby.
Fountainstown experienced a persistent low level of pollution throughout the season, he said.
Dr Lehane added that local authorities are investigating the Ballyheigue result, which was very uncharacteristic, as it has always met the highest standards.