Fingal County Council has erected a temporary ‘do not swim’ notice at Claremont Beach, Howth.
The ban, which is in place for the next 72 hours, is due to suspected contamination of the water from animals and birds and from urban surface waters discharging into the bathing water.
Further testing was taking place on Tuesday and the results of laboratory analysis will be available on Thursday. If the tests come back clear, it is hoped that the beach can then re-open for bathing.
Bathing water samples have been taken fortnightly at the beach since the summer bathing season commenced and the water has been at an “excellent” standard in each test, the council said.
The beach remains open but those visiting are asked not to swim as the notice has been put in place to ensure the health of bathers is not compromised, it added.
Members of the public intending to enter the water at any beach in Ireland are advised to check the water quality in advance. This can be done through the Envrionmental Protection Agency website www.beaches.ie