Swimmers treated for hypothermia after Bondi summer swim

An annual swimming event at Sydney's Bondi Beach has led to an ocean recovery effort, after competitors began showing signs of hypothermia.

The annual Bondi to Bronte Ocean Swim started at 9.30am, where clear blue skies were putting on a dazzling display above Sydney's most famous beach.

But the water temperature was a low 15 degrees – seven degrees below the December average.

As a result, some of the event's 1300 participants needed to be pulled from the water while others didn't feel the effect of the cold water until only after they had passed the finish line.

Competitors unable to make it to Bronte were attended by paramedics on Bondi Beach and wrapped in towels and thermal blankets.

Twenty-five swimmers in total required treatment, 12 of those for hypothermia with three transported to hospital for further care.

Ambulances lined the Bondi promenade, with paramedics erecting a triage tent in order to accommodate all those affected.