Rik O'Barry trained one of the worlds most famous dolphins, TV star Flipper, but he now thinks it's cruel to take dolphins out of the sea for tourists to swim with.
"Taking them away from their families, putting them in a cage and they're going to teach somebody about their respect for nature," said Mr O'Barry.
But the people who run the park say the dolphins are treated fairly and letting people swim with them is good because people can learn more about them in a more natural environment.
'Dolphins aren't pets'
Some holiday makers were upset when they learned the truth:
"They're not a pet or a toy - they're wild animals and they should be treated like that," said one boy on holiday near the park.
Campaigners say they'll do all they can to get parks that offer the opportunity to swim with the mammals closed down.
They say visitors get to enjoy one day, but the dolphins face a lifetime in captivity.