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.
Irish Coast Guard, RNLI and Water Safety Ireland urge everyone to 'Unite to Turn the Tide
July has been one of the busiest months in years for rescue services, with warm weather bringing more people to Wicklow beaches, rivers and lakes.
Bray Wanderers Head To Cobh Amid Apparent Cross-Channel Interest In Seagulls Talent
New Laws Boost Protection In Wicklow Mountains National Park
A dedicated National Parks Bill will put nature conservation first and help manage growing visitor numbers.
Woman Dies In Waters At Wicklow Beach
The incident occurred on the outskirts of Wicklow town, near the Blainroe golf club.
Wicklow Housing Remains Ireland's Most Expensive Outside Dublin
Strong demand, low vacancy and limited housing stock are keeping county prices elevated.
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