Prohibition notices were erected at Portmarnock and Claremont Beaches on Friday.
The notices are due to urban wastewater stormwater overflows posing a risk of pollution to bathing water quality at the beaches and are expected to last five days.
Both Claremont Beach and Velvet Strand Portmarnock remain open, but beach goers are asked to respect the do not swim notice to ensure their health is not compromised.
Members of the public can check for water quality at any of the monitored bathing waters in Ireland in advance by accessing the EPA website at www.beaches.ie or by checking the notice board at the entrance to each beach.
