Some of the golf balls found by divers in the Marlborough Sounds on January 23.

A group of divers were bewildered when they found 40 golf balls in a Marlborough Sounds marine reserve.

Among stunning sea life, divers found the golf balls concentrated near a King Shag colony in Double Cove.

Waikawa Dive Centre owner Stuart Scaife took to Facebook after their discovery, asking the public if someone had been aiming for the rare nesting birds.

DEBBIE GODSIFF The golf balls were found among sea life in a Marlborough Sounds marine reserve.

One commenter responded, claiming they hit the golf balls from their bach across the bay, in attempt to make the full 250 metre distance.

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"We have never had any intention of hurting any shags nor have [we] hit one in the past. Hope we can continue to do this in the future with no environmental damage," he said.

SCOTT HAMMOND/STUFF The golf balls were discovered under the nesting ground of rare King Shags in the Marlborough Sounds. (File photo)

Scaife asked if there would be more golf balls down there, suggesting they could do another dive to clean them up.

"There will be about another 3000 down there. Could they please be returned to our jetty?" the commenter said.

According to Stanford researcher Matthew Savoca, modern golf balls are made of a polyurethane elastomer shell and a synthetic rubber core. Manufacturers add zinc oxide, zinc acrylate and benzoyl peroxide to the solid core for flexibility and durability. These substances are also acutely toxic to marine life.

DEBBIE GODSIFF A fanfish pictured on the same dive trip as the golf balls were found.

When golf balls are hit into the ocean, they immediately sink to the bottom. No ill effects on local wildlife have been documented to date from exposure to golf balls. But as the balls degrade and fragment at sea, they may leach chemicals and microplastics into the water or sediments.

Scaife was concerned the golf balls seemed to be concentrated near the King Shag colony, which just "didn't sit right".

"Particularly in a marine reserve where the intent is to look after the fish life, to have this activity going on, which can only harm the sea life."

DEBBIE GODSIFF A fish peeks back at the diver.

He wondered whether to bring it to council attention.

"I don't own the sounds. I'm just an interested party that likes to keep it going. We see a lot of stuff that people don't see, we see it from a different perspective perhaps."