The oldest Indian Ocean bottlenose dolphin to be born and bred in captivity died at Port Elizabeth's Bayworld oceanarium late on Thursday afternoon, Bayworld spokespeson Eluise Matthys said.
There are as yet no physical indications of what may have caused her death.
An autopsy had been performed and tissue samples had been sent away for analysis.
"They are all very shocked. Some of them dedicated their lives to her," Matthys said of the oceanarium's staff.
"Dolly was an icon for Port Elizabeth. She's always been there and although she was old it happened so suddenly," she said.
"She had her own character. Dolly was well known for doing what she wanted to do, she was a very special lady."
She is survived by her three calves, Domino, Thumzi and Dumisa.
Dumisa, born in September last year, was still suckling.
The oceanarium's staff are now concentrating their energies on ensuring her well-being, introducing her to fish while feeding her electrolyte solutions.