Miracle the penguin took the plunge for the first time after spending his first weeks on land.
The penguin was abandoned as an egg by his parents but was rescued and hatched at Drusillas Park in Alfriston. Penguin keeper Emma Fluke hand-reared the bird.
Yesterday Miracle waddled into the water and was introduced to the other Humboldt penguins at the park.
Emma said: "He was a bit timid. He has seen other penguins through a wire fence but this was his first time in the water.
"Penguins know how to swim instinctively but it will take him a while to perfect his technique.
"There was no problem with the other penguins. I'm sure there will be a few scuffles in the future and Miracle will have to stand up for himself. But that's life."
Emma said she found the egg on June 16.
She said: "It was one of two eggs laid by its parents. They were first-time parents and after the first egg hatched they did not know what to do with the second.
"I was not that hopeful of him surviving and we were surprised when he did. The curator said it was a miracle - and the name stuck."
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