Rarotonga comes alive with the massive Cook Islands Triathlon this weekend.

The action kicked off in the water at Trader Jacks with the Boiler Swim on Thursday afternoon.

About 70 keen swimmers braved strong swells and clusters of coconuts as they swam wide to avoid them at Avarua.

The swimming competition, which is an optional event for the registered triathletes started about 5 pm.

Kiwi visitor Bex Grace took first place in 13 minutes 50 seconds.

It was her first time taking part in the Boiler Swim as she is on Rarotonga visiting her sister.

Grace, from Auckland, said she loves taking part in triathlon events.

The Boiler Swim is an ocean swim of around 800 metres – an out and back around the protruding remains of the SS Maitai.

It starts and finishes from the shoreline in front of Trader Jacks.

According to the organisers, it is a popular event for triathletes who have just arrived in Rarotonga.

It also is well attended by locals and any visitors who happen to be on the island and fancy a challenging swim.

The event is open to anyone. Supporters, local residents and anyone else visiting Rarotonga are all welcome to join the fun.

New Zealand Olympian Nathan Richmond holds the course record of 9 minutes in the boiler swim. He set this time in 2001 under exceptional conditions.

Meanwhile, the big action starts on Saturday with the Triathlon Festival at the Titikaveka Triathlon Site.

The transition area is set to open at 11.30am with a race start scheduled for 1.30pm.

It will be followed by a prize giving awards dinner at the Edgewater Resort & Spa on Sunday afternoon.