A Bay of Plenty girl is in intensive care in an American hospital with brain damage.

11-year-old Alyssa Ledbetter was swimming with her family on July 21 when she emerged from the water complaining of a headache, neck pain, blurry vision and numbness in her legs.

Alyssa was taken on a stretcher to the lifeguard station, where her condition deteriorated, her father Dave Ledbetter says in a post on a crowd-funding page.

Ledbetter says his daughter then lost control of her bodily functions and seizures set in.

Her blurred vision worsened, she couldn't recognise the people in the room, and she began to fall in and out of consciousness.

Alyssa was taken to a nearby hospital, where she underwent surgery. Surgeons drilled through her skull to drain the fluid and relieve pressure.

The Ledbetters, from Whakatāne, were told that Alyssa had two arteriovenous malformations in the frontal cortex of her brain.

'Alyssa suffered a subarachnoid haemorrhage when the weakened blood vessels in her brain ruptured and burst from the high pressure of blood flow from the arteries, causing bleeding into the brain,” says Dave.

"The neurological doctors have determined that open brain surgery is not an option, as the AVM is too deep inside her brain and the risk of permanent damage is too great - the only other realistic option is gamma knife radiosurgery."

The cause of AVMs is not clear, according to information on the American Heart and Stroke Association website.

Most people are born with them, but they can occasionally form later in life. They are rarely passed down among families genetically.

Some people with brain AVMs experience signs and symptoms, such as headache or seizures. AVMs are commonly found after a brain scan for another health issue or after the blood vessels rupture and cause bleeding in the brain, as in Alyssa's case.

Once diagnosed, a brain AVM can often be treated successfully to prevent complications, such as brain damage or stroke.

​Dave says Alyssa remains in the intensive care unit.

"This is a long slow process ... once discharged from hospital, she will have to complete outpatient treatment before she is cleared to fly to New Zealand.”

"Once in New Zealand, Alyssa will have to wait at least three to six more months for her brain to heal sufficiently before she can undergo gamma knife surgery."

"Unfortunately there is no gamma knife surgery available in New Zealand. The closest is in Sydney, Australia. One or more trips to Sydney may be necessary.”

Dave says his daughter is an exuberant and loveable 11 year old.

"She has always been a healthy and active child who loves hip-hop dancing, various sports including field hockey, swimming and surf-lifesaving with her family."

The family is raising funds for medical expenses, including the gamma knife surgery, ongoing CT and MRI scans, medications and various travel and accommodation expenses.

-Stuff