Alex Weber, an avid free diver from California, was swimming off Pebble Beach two years ago when she discovered thousands of golf balls littering the ocean floor.

"You couldn't see the sand. It was completely white," Weber, who was 16 years old at the time, told the NPR program "All Things Considered."

The golf balls ultimately came from five nearby courses, including Pebble Beach Golf Links, host of the PGA Tour's annual AT&T Pebble Beach Open Pro-Am.

This inspired Weber to start what she calls "The Golf Ball Project." With help from her father, Stanford University scientist Matt Savoca, and Pebble Beach employees - who began retrieving balls from beaches near their course at her encouragement - she was able to collect more than 50,000 balls over the next two years.

"Whenever we had good conditions, we were able to pull out between, like, 500 to 5,000 golf balls," Weber said.

As noted by Weber and her team in the journal Marine Pollution Bulletin, per NPR, golf balls contain toxic zinc compounds and are coated with a thin layer of polyurethane that degrades over time. As the balls degrade, they turn into microplastic pieces that marine animals could ingest.