A man has spent $2000 on his dog after it swallowed a discarded fish-hook while walking along the western bank of the Whanganui River.

The NZ Herald reports City Gym co-owner Pat McNamara was walking his two dogs, Cooper and Sabbath, along the boardwalk near the BP petrol station three months ago.

He noticed a piece of nylon hanging out of Cooper's mouth.

"I opened her mouth up, but I could not see anything apart from nylon, so I knew there was a hook," Mr McNamara says.

A vet referred Cooper to the Massey University campus in Palmerston North as the fish-hook was lodged down the dog's oesophagus near her heart.

Surgery costs started at $4000 but thankfully, this wasn't necessary, Mr McNamara told the Herald.

Vets were able to remove the hook with long tweezers using a endoscopic camera.

The three-and-a-half hour procedure cost Mr McNamara $2000.

Several fish-hooks have been found in the area by people walking their dogs.

They are believed to have been thrown away by people fishing along the western bank of the Whanganui River.

Mr McNamara says Cooper recovered quickly from the procedure but he thinks fishermen need to be more careful with their hooks.