Swimming has been temporarily prohibited at Killiney Beach in south Dublin following a suspected wastewater discharge into the sea.
Dún Laoghaire Rathdown County Council said it believed the wastewater flow had occurred in the vicinity of the popular bathing spot on Thursday.
Officials moved to close bathing, placing a number of a prohibition notices in the area which they said would remain in place until Monday.
The situation is now being investigated by local authority engineers who have taken water samples. The council said further updates would be posted in due course.
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The Health Service Executive has also been notified of the situation.