The incident happened off Wexford's Hook Head this evening.
The father of four in his forties was taking part in an underwater search for a fisherman who went missing from a trawler off the Saltee Islands yesterday morning.
The alert was raised shortly after noon today as he returned to the surface after a dive.
He was treated by colleagues at the scene and airlifted to University Hospital Waterford where he has since been pronounced dead.
Old Recording Adds To Intense Concern About Road Safety
Wicklow Farmers Praised & Reminded About Vigilant Pesticide Use
Matchroom Tee Up Katie Finale With Astonishing Promo Video Narrated By Barry Keoghan
Term Time Begins As Over 31 Thousand Go Back To School In Wicklow
Lidl Renames Its Boghall Road Outlet 'The Katie Taylor Lidl Store'