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.
Woman Dies In Waters At Wicklow Beach
The incident occurred on the outskirts of Wicklow town, near the Blainroe golf club.
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Love Songs on the Coast
Sunny intervals
High: 21°C | Low: 14°C
Sunny intervals
High: 20°C | Low: 13°C
Sunny intervals
High: 22°C | Low: 12°C
Sunny intervals
High: 24°C | Low: 11°C
Sunny intervals
High: 25°C | Low: 12°C