It is understood the alarm was raised after she failed to return from a swim.
A search was carried out and the woman was taken from the water shortly before 11pm.
She was taken by helicopter to University Hospital Galway where she was pronounced dead in the early hours of this morning.
Woman treated after Comeragh rescue
A 59-year-old woman has been rescued from the Comeragh Mountains in Co Waterford this afternoon.
It is understood the woman was walking by Mahon Falls when she sustained injuries to her lower leg.
South Eastern Mountain Rescue were alerted at 1pm this afternoon and the woman was taken by ambulance to Waterford Regional Hospital where she is being treated.
