She swam at her 32nd beach yesterday, at Narrow Neck on the North Shore, and plans to complete her task by the end of next month.
"I was thinking about water safety ... kids not being able to swim, schools taking out their pools and last year, when there were so many drownings," Mrs Burrell said.
"That's how I came up with Swim50 - swimming at 50 different beaches, one for every year of my life, spreading the water safety message and raising funds for charity."
Mrs Burrell said she was inspired by a story she heard about an 80-year-old man who had decided he wanted to play bowls for 80 days - one for every year of his life.
"I thought, 'If he can do that, I can do something too'."
Mrs Burrell spends about half an hour to an hour swimming at each beach and sometimes travels to several in one day.
She is sometimes accompanied by members of her family and friends and she has also made up T-shirts with the slogan "Swim50" to help raise funds for the Cancer Society.
Her aim is to get $5000 for the charity.
Mrs Burrell said she hoped what she was doing would inspire people not only to donate to the Cancer Society, but also to be more aware about being safe in the water.
She also hopes others are inspired to challenge themselves, after seeing what she is doing.
"I'm not a competitive swimmer ... It's not just about me.
"It's about the wider idea that if people can look at me and say, 'Wow, if she can do that, then I can do this', then that's a whole new level and that's very cool."