Acting Sergeant Steve Griffiths, of Balclutha, said the man and the teenage boy made it to shore, and the teenage girl was reported as missing.
All three were wearing life jackets, Mr Griffiths said.
The Otago Regional Rescue Helicopter helped to search for the girl, who was found on the shore about half an hour later.
Mr Griffiths said CPR was carried out but the girl could not be revived.
It was windy at the time of the accident and people described the conditions as rough.
A small crowd of holidaymakers and locals quietly watched the rescue operation from the beach and the nearby settlement of Newhaven.
Mr Griffiths said he wished to thank those who helped.
About six police officers, the Owaka Volunteer Fire Brigade, Catlins Marine Search and Rescue and St John staff from Owaka and Balclutha joined in the rescue effort.
- Otago Daily Times