The opening day of the popular three-event series in Port Fairy attracted 319 swimmers and the Warrnambool leg this Saturday is expected to attract another bumper crowd.

"We had a record at Port Fairy which follows on to us and there usually is a lot of registers for our part of the series, which is a positive sign for us and the series," O'Brien said.

Online registrations are open until 4pm on Friday. Participants can still sign up to compete on the day.

The weather forecast is looking favourable for the popular ocean swim, which offers a full course swim of 1.2 kilometres and a 500-metre short swim.

The Bureau of Meteorology predicts a cloudy day with a top of 23 degrees and a 20 per cent chance of rain.

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O'Brien encouraged swimmers to commit to the second leg of the swim series, which has been running since 2004.

"If you have ever wanted to try one now is a good time to do it when there is plenty of water safety around and it is a safe environment," he said.

"There is also the shorter 500-metre swim so If people have ever yearned to do it, now is a good opportunity."

The swim series is a major fundraiser shared equally between the Port Fairy, Warrnambool and Port Campbell surf lifesaving clubs.

It contributes to their combined duty to patrol the south-west's beaches over summer and all year round.

Last year Sophie Thomas took out the overall win and was the first female across the line for the the Tony Ryan Memorial Bay Swim.

Sebastian Christie-Crane was the first male to cross the line, finishing 22 seconds behind Thomas.