At Belmore Basin, hundreds lined up after months of training to take part in the 12th annual Illawarra Aquathon. From triathletes to mums and dads, you had to be in it to win it and competitors showed true Aussie gusto as they paddled and pounded the pavement around courses ranging from a 150m swim and 2km run to a challenging 900m swim and 7km run. The weather even obliged with a light drizzle to keep the competitors cool.

And although the water was chilly and the courses were gruelling, it was all for a good cause, as more than $20,000 in donations rolled in for Anglicare and a range of other charities.

As the sun came out and crowds headed to the foreshore, the day's events took a quirky turn, including blow-up boat races and a fiercely contested sandcastle-building competition.

The highly anticipated thong-throwing competition even had a celebrity drawcard, as former Australian cricket captain and one-time Australian of the Year Steve Waugh swapped a ball for a flag-emblazoned thong.

In between throws, Waugh said the Gong was an ideal place to celebrate the national day.

"I think it's just a great day - families and kids on the beach, laughter in the air and the smell of barbecues in the air, that's what reminds me of Australia," he said.

There was also a touch of the traditional as Concord Concert Band led a march up Cliff Rd to Gun Battery Park for a ceremonial cannon firing and an explanation of the park's history.

Little Aussies were kept entertained throughout the day at the McDonald's children's stage by groups including Monoxide's Half High Circus, Ronald McDonald and friends and Southside Modern Jive.

Flagstaff Hill was the musical hub, with acts such as the Elemental Grooves and IRISchild taking to a stage with a view overlooking Belmore Basin.

The day went out with a bang when a fireworks extravaganza lit up the skies at 9pm, delighting onlookers.