The event, organised by the Southern Lakes Swimming Club, will see members and supporters do laps of the pool for 24 hours, aiming to collectively complete 10,000 lengths - or 250km - by noon tomorrow.
Joining in were local free divers who are completing under water laps in an adjacent lane.
Club president Sheena Ashford-Tait aimed to raise $2500 for St John - that target was reached about 10 minutes before the horn sounded to signal the beginning of the event.
Swimmers will camp in Alpine Aqualand overnight - anyone was welcome to come and swim laps for the cause - but after 8pm, when the facility closed to the public, only members of the club were able to participate until it reopens tomorrow morning.
Lane time had been donated by Alpine Aqualand, which has also put on two lifeguards for the duration of the event.
• To donate, visit https://givealittle.co.nz/fundraiser/24-hour-swim-for-st-john
