09/22/2011 at 04:00 PM EDT
When Harry Connick Jr. first read the script for a movie about a dolphin who loses her tail but survives with the help of human friends and an inspirational will to live, he thought it had come entirely from someone's imagination.
"I was blown away to find out the story was real," Connick tells PEOPLE.
Not only was the story real, but the filmmakers also brought in the real-life dolphin, named Winter, to play herself in the movie. "I was just so thrilled to know that I'd be able to work with her," he says. "It was an incredible experience."
Throughout the filming process, staff from Florida's Clearwater Marine Aquarium, where Winter lives, were on hand to help Connick and his costars – Morgan Freeman, Nathan Gamble and others – interact with the dolphin, who swims with a prosthetic tail. But Winter could communicate with her human cast mates on her own.
"You kind of think she does know the effect she's having on others," Connick says. "And then you catch yourself and say, 'Well, wait a minute – she's a dolphin!' But then she has this look in her eye that would lead you to believe she has otherworldly awareness. It's profound being around her."
Connick had to learn to be in the water with Winter and how to feed her with a bottle, but the biggest challenge was putting the prosthetic tail on her.
"That was a daunting task," Connick says. "She's a big animal, she's very powerful, she's suffered a lot of pain and trauma. You're not sure if you're going to hurt her. And you get the sense that she was like, 'You know what? I know you don't know what you're doing, but let's work together on this.' Those are the kinds of things that you don't forget very easily."
Something else Connick won't forget? The scent of the marine aquarium. "Oh, man, it's pungent," he says. "You walk into that marine aquarium and you know you're in a marine aquarium. It's a very strong smell."
Dolphin Tale opens in theaters Friday, Sept. 23.