"The day I was diagnosed, there were seven other people diagnosed in New Zealand. Every day there are seven women or men diagnosed with breast cancer."
Hall received rapid treatment that was successful, and is in remission. As part of her treatment she did a swimming-pool based therapy programme designed to increase her range of movement. That led her back to swimming, something she enjoyed as a teenager. Hall says finding a sport has been an important part of her recovery from cancer.
"You complete your treatment, and that's a milestone," she says. "Then I think it's up to you as an individual to keep going.
"For some people it might be a change in lifestyle, it might be looking after your health better. For me it was going back to my fitness."
Getting back into the water wasn't all plain sailing, however.
"I started with not being able to swim very far," Hall says. "I could probably only swim about 300m, and every single stroke my arm was sore. I then had treatment for lymphoedema and improved."
Hall trains in the open water near her Kohimarama home and also at the Parnell baths. She says her stamina has built up steadily, and she can now swim about 1.2km at a time. She hopes her story can inspire other people recovering from cancer to embrace an active lifestyle.
"Lots of people come through a rough diagnosis and treatment. They come out of it thinking, 'what can I do to maximise my long-term health?'
"You've got to find an activity you enjoy. The key is to start building up slowly and regain your body's energy. When you've been through radiotherapy and chemotherapy fatigue is a big thing.
"You need to be grateful you've got through it and minimise the risk of recurrence as much as possible. For me, that's being mentally and physically strong."
Scott Rice, the organiser of the King of the Bays event, says he hopes Hall is able to raise as much money as possible for Sweet Louise.
"Our series is all about giving it a go, " he says. "Sinda's extraordinary efforts in overcoming adversity make her a fantastic role model."
King of the Bays
When: Saturday, April 18.
Distances: 2.8km, 1000m and 300m courses. There is also a 200m course for children.
For more information, click here.
To donate money to Sweet Louise, click here.