A baby dolphin died in the middle of a performance in the city of Varna on the Bulgarian Black Sea earlier this month.
An autopsy gives result that the dolphin was 'overworked' and 'stressed'.
Spectator Bisser Lyubenov told BBC "There was a disturbance, the dolphins stopped playing and performing tricks and then that's when they asked the audience to leave."
Some people recall that they could see the lifeless body of the dolphin from the park's cafe.
The dolphinarium denies that the dolphin died during the middle of a performance in front of children, but witnesses state otherwise.
A biologist that works with the attraction stated that the baby and mother were separated at birth.
"You can't have a mother leaving its child in order to take part in the show. This can happen about six months after birth." Tsvetan Stanev tells BBC, "A baby dolphin taking part in performances nine days after it was born - this has never happened in this dolphinarium."
Animal protection expert, Yavor Gechev explained "This means categorically that the conditions don't meet even the minimal standards for keeping such animals. The animals are struggling there, they are not surviving."
Dolphin lovers and activists are calling for the park's closure, even signing online petitions.
Reports show that five dolphins and a sea lion have died in the park's care in the past five years.