"She helped out - she did great work. Other patrons helped out. We closed the pool once CPR was underway," he said.
"By all accounts staff, other pool users, ambulance staff - everyone did their best to try and revive her but unfortunately it didn't happen."
An ambulance was called by a member of the public who reported a person had drowned, a central ambulance communications centre spokeswoman said.
Lifeguards used a defibrillator on the woman before ambulance staff arrived, Wellington Free Ambulance spokesman Daniel Paul said.
Paramedics gave the woman further cardiac arrest treatment, including more defibrillator treatment, but it was to no avail.
Wellington police spokesman Nick Bohm said police, ambulance and fire services all responded to the incident.
He said emergency services and the registered nurse, who lent some valuable skills, spent "a considerable amount of time" trying to revive the woman.
"But unfortunately, despite the skills and efforts of everybody there, their efforts were unsuccessful."
Mt Bohm said the matter would be referred to the coroner.
"At this stage there are no suspicious circumstances around the death. It looks like she has come to grief while in the water, rather than a drowning."
The woman's name would be released once next-of-kin were informed.
Mr MacLean said the pool has been closed this morning and the staff who were directly involved in the incident had been stood down.
"Everyone here is obviously very upset about what's happened, but we're offering the staff counselling," he said.
The pool was not expected to re-open until later this morning or around midday, when other staff would be available.
