A boat carrying four people capsized at Taieri Mouth in South Otago on Friday.
A member of the public told police that a two-metre alloy boat had overturned at about 9.15am.
One person required treatment at Dunedin Hospital for hypothermia.
Three of the boat's passengers had been swept out to sea and were winched to safety, while the fourth had made it to shore, Sergeant Craig Brown says.
He says the Dunedin marine rescue team was sent to the area in a helicopter to find the group.
Mr Brown says the conditions at Taieri Mouth were pretty choppy because of an outgoing tide.