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Divers in California have stumbled on an unexpected source of plastic waste in the ocean - golf balls that come from coastal golf courses. Golf balls contain plastic and can emit toxic chemicals. And as NPR's Christopher Joyce reports, there are lots of them underwater, something discovered by a 16-year-old diver named Alex Weber.

ALEX WEBER: My dad - he raised me underwater.

CHRISTOPHER JOYCE, BYLINE: Alex Weber is a free diver. She just holds her breath. In 2016 near Carmel, Calif., she and her father were diving in the Pacific just offshore from a golf course. She looks down and saw something weird.

WEBER: You couldn't see the sand. It was completely white.

JOYCE: Golf balls.

WEBER: You look down, and you're like, what are you doing here?

JOYCE: Thousands of golf balls.

WEBER: It felt like a shot to the heart.

JOYCE: She was offended. She decided she'd haul them up. She put them in her family's garage.

WEBER: I had all of these golf balls in my garage, and they stunk. And I had no idea why.

JOYCE: Then she heard about a scientist who studied plastic waste in the ocean. His name was Matt Savoca from Stanford University. She emailed him. He came to look at her collection.

WEBER: Fifty thousand golf balls just sitting in the garage. He said I should write a paper about this. And I was like, Matt, I'm 16 years old. I don't know how to write a scientific paper.

JOYCE: He said he'd help. That meant diving with her - not easy.

MATT SAVOCA: The oceans off California are actually quite cold, and so you suit up in a pretty thick wet suit. It's incredibly physically demanding.

JOYCE: They took kayaks out to ferry the golf balls back.

WEBER: We'll have the kayaks so filled with plastic that we'll end up just having to tow the kayaks back, and we'll have to swim it to shore.

SAVOCA: While we were out there, we would hear plink, plink, and then we'd look up on the hill, and there would be golf balls flying in off the course right into the ocean where we were doing some collections actually.

WEBER: Whenever we have good conditions, we're able to pull out between about, like, 500 to 5,000 golf balls.

JOYCE: Over two years, they found more than 50,000 golf balls. The source - five golf courses. Three were up the Carmel River. The golf balls just rolled under water down to the ocean. In the journal Marine Pollution Bulletin, the team says chemicals from 50,000 or so golf balls will probably only have a small effect on the ocean, but they do degrade into microplastic pieces that marine animals could eat. Alex Weber says if those golf balls floated, people would be shocked.

WEBER: If a person could see what we see underwater, it would not be acceptable.

JOYCE: Christopher Joyce, NPR News.

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