The woman, in her early 20s, was rescued by RNLI lifeguards who were on duty for the first day of the season at Newquay's Fistral beach.
Lewis Timson, lifeguard supervisor, said the surfer's longboard leash snapped while she was competing in the Natty Surf Jam one-day event.
He described conditions at sea as "pretty wild".
The "distressed" woman, who is thought to be from Newquay, was taken ashore, but was not believed to need hospital treatment.
The festival was arranged in memory of 25-year-old local surfer Nathaniel Loney who died after battling severe depression and bi-polar disorder.
The money raised is being given to the Invictus Trust, a charity which supports young people with mental health issues.
The rescue highlights statistics from the RNLI, which show a big increase in the number of incidents around the South West.
Last year, beach lifeguards dealt with more than 11,000 incidents, while lifeboat crews launched 1,614 times - a 35% increase from the previous year.
There will be full-time lifeguard cover at Fistral and Croyde in Devon until the end of the season, with a number of other beaches in Devon and Cornwall patrolled during the Easter school holiday period.

8 August 2016 Last updated at 10:28 BST

Too many over-65s end up in accident and emergency unnecessarily, says the NHS Confederation's Commission on Improving Urgent Care for Older People.
The group said this was because of a lack of help when they fell ill.
It called for radical steps, including providing urgent care at home and getting doctors to carry out "ward rounds" in care homes.
The commission's report said older people were "poorly served" and "all too often forced to go to A&E".
And once in hospital, they faced longer stays and losing some of their independence.
The report said older people needed more help navigating the complexities of the health and care system.
It pointed to an Age UK scheme in Cornwall, where the frailest people had co-ordinators helping organise their care.
It also said GPs could identify and work with patients most at risk of hospital admission.
The report also highlighted a scheme in north-east London, where hospital and ambulance staff were working together to provide emergency care in people's homes.
Nurses and paramedics assess and treat older people who have fallen but not suffered a fracture.
Equipment, such as walking frames, can be arranged.
And from April to July last year, seven in 10 of the patients seen had stayed at home.
Another project highlighted was in Hertfordshire, where GPs visited care home residents on a regular basis, with rapid response teams on call to attend to residents who needed urgent help.
Source: Commission on Improving Urgent Care for Older People
Dr Mark Newbold, who chairs the commission, said: "Older people do need to access A&E at times, and the best hospitals tailor their service to meet their needs.
"But all too often, older people are forced to go to A&E because the alternative services that would help them be cared for at home are not available at the time they need them."
A spokeswoman for the Department of Health in England said the government was fully supportive of the ideas put forward.
She pointed out a pot of money known as the Better Care Fund - amounting to Â£5.3bn this year - had been set aside to fund schemes largely focused on keeping people out of hospital.
The vision of improving care for older people was "being realised", she added.
Meanwhile, the Local Government Association has called for more to be done to tackle loneliness, now a "major public health concern".
Councillor Izzi Seccombe said it was increasingly being reported as an issue among older people referred to councils for care.
She said the solution lay in supporting befriending schemes and those that tackled social isolation, many of which were run by the voluntary sector.
"The impact of loneliness can be devastating," she added.
A woman has been rescued from the sea after getting into difficulty during a charity surfing festival in Cornwall.
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Older people in need of urgent help are being failed by the NHS, a group of English and Welsh health leaders say.