When Matt Eaton went fishing on Otago Harbour yesterday, the last thing he expected to return with was a tourist's passport.

The 36-year-old was on a boat with his boss and some friends near Otakou about 4.30pm yesterday, "just cruising along that side of the harbour" when they saw the Otago Regional Rescue Helicopter fly over and a fire engine driving around the road.

"We thought 'what's going on here?'."

Unbeknown to them, a car had slipped on the greasy road and gone into the harbour.

The driver swam to shore after his car went into the harbour. Photo / ODT
The driver swam to shore after his car went into the harbour. Photo / ODT

"When we got there, a fireman was standing on the road, pointing, and we saw a car under the water."

The uninjured Scottish driver managed to escape from the submerged car, but his passport and luggage remained in the vehicle.

When it became apparent someone would have to retrieve it, Eaton drew the short straw and volunteered.

He stripped down and dived in.

"The boat said the water was 15.5C, but it felt a hell of a lot colder than that."

As well as carrying the driver's luggage and passport, Eaton swam ashore with an umbrella and a roll of toilet paper.

"I asked him [the driver] if he wanted the toilet paper and he said: 'It's a bit late now'."

Sadly, that was what the catch of the day amounted to, but Eaton was pleased with his effort and delighted he could help someone having a spot of bad luck.

"There would be nothing worse than losing your passport.

"You can replace clothes but it's hard to replace a passport when you're in a foreign country."

A St John spokesman said no one was injured and the helicopter was stood down.