Some of the world's best triathletes will compete in the 2015 Australia Day Aquathon, but for many the event isn't about crossing the line first.

Since 1999, the nation's biggest swim and run event has seen thousands of local competitors dive into Belmore Basin to kick off the day's celebrations.

Event Organiser Rob Battocchio expects 2015 will be no different.

"The Aquathon is about community. It creates an amazing atmosphere that adds to the Australia Day festivities," he says.

"To witness first timers, hundreds of children, seniors, and people with a disability all enjoying themselves is the real win of the day."

The 2015 instalment sees the return of the usual elite divisions, beginning with the Long Aqua (900-metres swim and 7-kilometres run) at 8am.

It will also include the first Ladies Try-Aqua.

The event is a shorter crash course of what the Aquathon involves and is designed to bring greater participation numbers.

"The Aquathon is about participation, and designed for all ages and standards: safe and fun," he explains.

Battocchio says the event is also a great opportunity for competitors to "rub shoulders" with a number of elite triathletes.

Commonwealth Games bronze medallists Aaron Royle and Ryan Baillie will compete, as will women's world No 1 and two-times defending champion Gwen Jorgensen.

Registration is still open for competitors on Saturday at www.aquathon.com.au.