Mr Butcher, who works as an animal control officer during the week, said he saw a police car arrive quickly. "I don't know who called the police, but they arrived quick."
He said he looked over the edge of the wharf and could see the woman "clinging on to a boat rope".
"I could see a police officer in the water holding the woman's head up.
"I slipped off some clothing and just jumped in too," he said.
"It was freaking freezing. As soon as I jumped in, the water zapped all my energy."
Mr Butcher said he helped keep the woman's head above the water while emergency services on the wharf worked out how to get her out.
A rope was lowered down to the group and the police officer and Mr Butcher tied it around the woman so she could be winched up to safety.
"She wasn't talking, she was not coherent," he said.
After the woman was safely out of the water, Mr Butcher pulled himself up a nearby boat ladder and climbed to the top of the wharf. The police officer swam to a spot where he could get out of the water safely.
Mr Butcher was suffering from hypothermia from the cold water, he said. "Time went by so fast, but the water was cold ... [in the ambulance] they stripped the clothes off us and put us in a bed that had fan heaters and things to warm me up and raise my body temperature."
He said that when he got home about 4am yesterday his body was still shivering.
"I don't know what happened to [the woman]. I hope to find out," he said.
Napier police could confirm the incident happened, but said that other than a constable assisting with "fishing" someone out of the water, details were "very vague".
A Hawkes Bay District Health Board spokeswoman said the woman had been discharged from hospital yesterday.
