About 15 dolphins joined swimmers at the Island Bay Festival swim to Tapu Te Ranga island.

Swimmers taking part in the Tapu Te Ranga Island swim in Wellington's Island Bay were joined by about 15 dolphins on Sunday morning.

Sam Davis was among the crowd of onlookers delighted by the dolphins' appearance alongside more than 70 swimmers.

"There was one pod to start with, of about six, then a second pod joined in as the race was going on. There were about 15 in total," he said.

SAM DAVIS "I think they could hear the swimmers, so they cruised over and kind of joined in," witness Sam Davis said.

"It looked like they were fishing in a different part of the bay to start with.

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"Then I think they could hear the swimmers, so they cruised over and kind of joined in. They got nice and close to the rescue boats too.

SAM DAVIS The swimming race was part of the nine-day Island Bay Festival.

"It looked like they were just mucking around with the swimmers, then they had a play with some of the surf-lifesavers who were on their paddle boards, then they just branched off around the back of the islands and went back out to sea again."

The island swim was part of the nine-day Island Bay Festival, which began on Saturday.

On Friday afternoon a pod of about six or seven dolphins was spotted swimming through Oriental Bay.

Less than four weeks ago, a large pod of dolphins, which some said was close to a hundred, stunned swimmers and onlookers in the same body of water.

They were thought to be common dolphins, which were spotted about twice a year in Wellington Harbour, but not usually at Oriental Bay.