The event is Stockton Surf Life Saving Club's largest annual fundraiser, with all money raised going towards life saving equipment.

Stockton is the second oldest surf club in the Hunter branch, formed on January 15, 1908, just five days after Newcastle.

The club traces its history back to the early 1860s with the Stockton Rocket Brigade, a group of men devoted to rescuing seafarers who became shipwrecked trying to enter Newcastle Harbour.

Historical records show the men, who crewed the Rocket Brigade rescue boats, were the same men who later formed the surf club.

Once a year Stockton SLSC gets permission to allow swimmers to legally cross the world's largest coal port, when the harbour master halts shipping.

The annual Australia Day swim features a social single crossing of the harbour, or 700 metre swim, starting from Stockton at 10am and double crossing race of 1400 metres starting from Queens Wharf at 11am.

Male and female 1400m winners receive $1000 each, second $500 each and third $250 each, making the swim one of Australia's richest open water events.

Water-safety staff on boards, jet skis and rubber duckies accompany swimmers across the harbour.

Newcastle-bred Olympic swimmers Thomas Fraser-Holmes and Justin Norris are both previous winners of the 1400m race.

Entries are open until midnight January 24, costing $75 for the 1400m event, compared to $100 on the day, and $65 for the 700m swim, compared to $80 on the day.

The 700m event is open to children aged 12 and 13 costing $55 for entries up to midnight January 24, compared to $70 on the day.

While participants can use swimming aids such as flippers and pool buoys, prizes and podium acknowledgement is only awarded to swimmers not using aids.

For more information and how to register www.oceanswims.com/event/newcastle-harbour-swim-classic/