Water Safety Ireland is appealing to swimmers and people taking part in water activities to take extra care over the festive season.
It follows the death of a swimmer in his thirties earlier this week at the Hawk Cliff bathing area on the Vico road in Killiney.
The Irish Coastguard were alerted on Wednesday afternoon, and Dun Laoghaire RNLI arrived at the scene and took the swimmer from the water to Coliemore Harbour, where medics were waiting.
But efforts to resuscitate the man failed.