Ruby was rescued by the crew on Port Nelson's pilot boat after being swept out to sea from a Nelson beach.

Mike Gafa wasn't worried when his border terrier Ruby plunged into the sea at a Nelson beach.

After all the six-year-old dog had swum at Tahunanui's back beach many times. But on Sunday afternoon it all went wrong as Ruby splashed into the Blind Channel at Parkers Cove.

"She's swum out a long way before but she's always come back," Gafa said. "This time the tide was at its peak going out, and she got out into the tidal rip. I turned to my wife and said to her 'she's not coming back, she can't swim against that'.

supplied Nelson man Mike Gafa with his border terrier Ruby who was rescued after being swept out to sea.

"The analogy is like sticking a twig in a river and watching it float away. She was moving about that fast."

He ran down the beach "in a bit of a panic", borrowed a kayak from a group of people, and paddled out to try to find her, but couldn't.

"I thought I'd seen a dead dog, it was just debris in the water, it happened about three or four times, so I was prepared for a dead body at any point. But then I thought, 'nah she's too good a swimmer'".

A man on the beach who worked for the harbour board rang the coastguard.

Fortunately for Ruby and her owners a Port Nelson pilot boat crew had just finished a shipping job and were in the area when they were alerted to Ruby's plight.

They quickly found the paddling dog about 800 metres out to sea, near The Cut, about two kilometres away from where she entered the water. Spotting the small, white pooch was helped by calm conditions.

Gafa said Ruby had been in the water for over an hour. She was "a wet little ball all wrapped up in a towel" and "visibly shaken up" when she was returned.

Gafa has had Ruby and another border terrier, Zac, since they were pups.

"We are so grateful and thankful. Without the people on the beach and the crew, we would never have got our little Ruby back."

The dogs were treated to their favourite bones on Sunday night and Ruby was "getting back to her normal self" on Monday, Gafa said.

Nelson harbourmaster David Duncan said it was the first such rescue he had heard of in his eight years in the role.

"The port is always willing to assist in search and rescue, especially where people are involved, but this was the first time that I know of we've done it for an animal."

"The weather was perfect, the dog and the owner were both lucky."