An online video shows a woman being attacked repeatedly by Dusty the Dolphin in Doolin County Clare.
The woman, who was pulled from the water and taken to the hospital, suffered a compressed vertebrae, broken rib and damage to her lung.
UTV reports that after several reports that the dolphin displayed aggressive behavior towards people, the local council and Irish Whale and Dolphin Group erected warning signs telling people not to swim with the dolphin. At least five other people have been hurt.
"If this continues, it may lead to a fatality and there will be strong pressure to remove or destroy the dolphin," said statement from the Irish Whale and Dolphin Group said.
"If you really are concerned about Dusty, you will not swim with her - or at least if you do, you should show her the respect a wild dolphin is entitled to."
"It is IWDG policy to discourage people swimming with whales and dolphins," the group said.
"The risk is not only to humans, but also to the dolphin - as habituation to humans increases risk of injury or death to the dolphin."