The NSRI said in a statement that it was called out to the scene at about 14:30 rescue swimmers were dispatched and the sea rescue craft Vodacom Rescuer II was launched.
A Police Sea Borderline boat, that was also carrying members of the Police Dive Unit, WC Government Health EMS, the SA Police Services and ER24 ambulance services also responded.
Upon arrival on the scene it was found that two boys and a girl, aged approximately 14 and believed to all be friends from Mossel Bay, had got into trouble while swimming.
An unidentified woman had rescued the girl from the water and had commenced CPR, but she was eventually declared dead.
The police boat had located the bodies of both boys in the water, but both had succumbed to drowning and were declared dead.
The bodies of the three teens were handed to Forensic Pathology Services and police have opened an inquest docket.
Family members of the children are being supported by police trauma counsellors.
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