Two separate investigations are under way into the circumstances surrounding the death of a coast guard volunteer off Co Clare yesterday.

The Marine Casualty Investigation Board and the Irish Coast Guard are investigating how Caitríona Lucas, who was searching for a missing man with two other volunteers, died when their rigid inflatable boat overturned in heavy swells. 

The 41-year-old mother-of-two was pronounced dead shortly after being airlifted from the water.

Her colleagues, a man and a woman who were later rescued, were taken to University Hospital Limerick.

Irish Coast Guard Voluntary Services Manager Declan Geoghegan said that one volunteer was still being treated in hospital and it was hoped she will be released later today, while the other was discharged from hospital last night.

Speaking on RTÉ's Morning Ireland, Mr Geoghegan said a short time before the incident, around midday, the crew had made radio contact to say they had completed their search for the person missing since Friday, and were returning to base.

He said the crew issued a mayday call soon after that.

Ms Lucas's husband Bernard is also a coast guard volunteer.

It is understood the mission Ms Lucas and her colleagues were on was for the "recovery" of the body of a missing man rather than a rescue.

A major search operation got under way after the boat overturned, which involved another unit from Kilkee and the rescue helicopter from Shannon.

The boat's coxswain was rescued from down a cliff in testing conditions, a Coast Guard spokesperson said.

Doolin Coast Guard, the RNLI and the Lahinch Surf Rescue Team and divers were also involved in the final rescue.

This afternoon, a former colleague of Ms Lucas has described her as a vibrant, dynamic person who gave 110% to everything she did.

Speaking on News at One, Clare County Librarian Helen Walsh said that pictures Ms Lucas had prepared for an upcoming Roald Dahl children's event are still hanging on the library windows.

Helen said that everyone is shocked and coming to terms with her death yesterday.

"I think for us, as library staff, Caitríona really is irreplaceable because she was so good in so many areas. All of our staff are so shocked. We're just coming to terms with it. So, you know, it's really just a shocking time for all of us and we're really just trying to process the whole thing."

The libraries Ms Lucas worked in were Ennistymon, Corofin and Lisdoonvarna.

These branches were closed today as a mark of respect and a decision around the closure of libraries will be made when funeral arrangements are announced.

Book of Condolences in Clare

Last night, Taoiseach Enda Kenny paid tribute to Ms Lucas, who said her death had cast a "dark shadow" over the country.

"The heroic work and selflessness of the Irish Coast Guard is well known around our coastline," said Mr Kenny.

"To learn of the death of Caitríona, and of injury to her colleagues brings home the real dangers our rescue personnel face and this awful news casts a dark shadow over people all over the island."