Swimming is prohibited at Claremont beach for two days, and an advisory notice not to swim at Malahide beach in north Co Dublin is in place for the next three days.
Do-not-swim notices were issued by Fingal County Council for 72 hours after samples taken on Tuesday came back with preliminary results of E. coli.
The initial advisory notice not to swim at Claremont beach has been replaced by a prohibition notice for a period of 48 hours, while the advisory notice not to swim remains in place at Malahide beach.
Malahide beach and Claremont beach met the standard for “poor” water quality.
All other identified bathing waters met the standard for “excellent” water quality and the next scheduled seawater.
Further testing is due to take place on Friday with the results expected on Saturday.
The beaches remain open but users have been advised to respect the notices, avoid swallowing or splashing water, to wash hands before handling food, avoid swimming with an open cut or wound, or if you are pregnant or have a weakened immune system.
Members of the public can check for water quality at any of the monitored bathing waters in Ireland in advance by accessing the Environmental Protection Agency website at www.beaches.ie or by checking the notice board at the entrance to each beach.