Emergency services and lifeguards rushed to the woman’s aid when she fell seriously ill on Saturday.
She was understood to have been with a young child when the incident happened.
Panicked guests hurriedly vacated the pool following a tannoy announcement ordering everyone to evacuate.
A witness told the Mirror that a lifeguard was trying to resuscitate the mum after she was pulled from the pool in front of a family member.
“We were in the pool session from 6 to 7.15pm. It must have been around 6.45pm. I was with my kids on the external water chute when there was a loud whistle and a message came over the tannoy telling everyone to get out of the pool,” the mum-of-two said.
“No-one knew what was happening. It was half term so the pool was busy. People were pulling their children out of the pool, there was a sense of panic.
“There was a young woman with a foil blanket around her holding a baby in her arms. It might have been the lady’s daughter. She looked like she was in complete shock.
"No-one would tell us if the lady was alright or not. But it didn’t look good. It was so shocking. She might have had a heart attack in the water.”
The woman was taken by air ambulance to hospital for emergency treatment on Saturday evening.
Her current condition is not known.
A spokesman for Butlin’s in Skegness told Lincolnshire World they were "continuing to support the family where possible".
“A guest staying with us fell ill within our swimming complex," the spokesman said.
“The guest was quickly attended to by lifeguards before being transferred to hospital. Our team are in contact with the guest’s family to offer our full support.”
An East Midlands Ambulance Service spokesperson said: "We received a call at 6.41pm on Saturday 5 June to Butlins resort in Skegness to assist with a medical emergency.
"We sent a paramedic in an ambulance car, two crewed ambulances and the air ambulance was also in attendance.
"We transported one patient to Lincoln County Hospital via air ambulance."