Balclutha police yesterday named the dead teenager as Eluned Jane Finney (13), of Balclutha.
Eluned was on the boat with her father - a 48-year-old Balclutha man - and a 13-year-old male friend on a fishing trip, headed towards Surat Bay east of Owaka on Wednesday afternoon on a 12ft (3.66m) aluminium boat.
About 300m from shore the boat's engine began to fail and then cut out.
The boat became swamped, before capsizing about 1.30pm.
Police said the man and the teenage boy made it to shore, and the teenage girl was reported as missing.
Eluned was found on shore about half an hour later, but was unable to be revived.
All three were wearing life jackets.
While the Finney family lives in Balclutha, Eluned was a pupil at Catlins Area School, in Owaka.
Principal Alex MacCreadie said she was a ''lovely kid'' who was involved in many areas of school life.
''A really nice, breezy kid ... she will be deeply missed.''
Eluned was very musical - involved with choir, the orchestra and kapa haka - and also played netball for the school.
She had been a pupil there for three years, and would have been year 10 this year.
''It's another devastating blow for the community ... we are still getting over the loss of Rowan [Parker].''
On Boxing Day 2012, Rowan Cai Parker (16) lost control of his quad bike and plunged off a cliff in the Chaslands area of the Catlins.
Mr MacCreadie described the school as a ''nice little tight-knit school'', and the wider South Otago community had rallied around the Finney family.
Acting Sergeant Steve Griffiths, of Balclutha, said the family appreciated all the assistance and support received, and had requested privacy from the media.
The death has been referred to the coroner.
Volunteers worked yesterday to recover the boat, but could not shift it from the sand bar, he said.
Catlins residents told the Otago Daily Times many boats had encountered difficulties on the sand bar over the years.
Surat Bay takes its name from the ship Surat, which was beached and shipwrecked there on New Year's Day, 1874.
