Mr McNamara took Cooper to the vet, but a decision was made to take her to Massey University in Palmerston North, where they have equipment necessary for such a delicate procedure.
The fish-hook was lodged far down Cooper's oesophagus, near the heart, making surgery a dangerous and expensive option.
Mr McNamara was told that that an operation would cost $4000.
Thankfully, surgery was not necessary. Vets were able to remove the hook using long tweezers with the aid of an endoscopic camera.
The procedure took three-and-a-half hours and cost Mr McNamara $2000.
It did not take long for Cooper to bounce back.
"I didn't come back [to the boardwalk] for a couple of weeks. I stayed away, but I like it here."
Mr McNamara was not bitter towards people who fish in the area; they were part of the reason he liked walking his dogs there.
"I think it is really cool when you walk along there. ... because there are retired guys and unemployed guys and young kids fishing with their fathers."
However, he said, some fishermen needed to be more careful with their hooks.
"Some of them leave their hooks and just don't worry about it. They probably don't think."
Wanganui District Council issues $100 fines for littering. A spokesperson said they were not aware of any other cases of dogs swallowing discarded hooks.