Scientists and volunteers who have spent the last month gathering data on how much plastic garbage is floating in the Pacific Ocean will return to San Francisco and share preliminary findings.

Volunteer crews on 30 boats have been measuring the size and mapping the location of tons of plastic waste floating between the West Coast and Hawaii.

Three of the boats, including a 171-foot mother ship, will arrive at San Francisco's Piers 30-32 on Sunday, when the next steps will also be announced. The boats went on a 30-day voyage as part of the "Mega Expedition," a major step in an effort to eventually clean up what's known as the Great Pacific Garbage Patch.

The expedition was sponsored by The Ocean Cleanup, an organization founded by Boyan Slat, a 21-year-old innovator from the Netherlands who first became passionate about cleaning the oceans of plastic while diving in the Mediterranean Sea five years ago.

"I was diving in Greece and realized that there were more plastic bags than fish, and I wondered why can't we clean this up," Slat said.

Slat dropped out of university after his first six months and has dedicated his life to developing the technology that he says can start removing garbage by 2020.

He has envisioned using long-distance floating barriers that will attach to the seabed and will target rotating ocean currents full of waste and skim garbage from the surface while aquatic life and the currents themselves pass underneath.

After his idea was shared thousands of times on the Internet, Slat decided to launch a kick starter campaign and raised $2 million euros (about $ 2.27 million) that helped to start his organization. Soon, his innovative solution got the attention of major philanthropists in Europe and Silicon Valley who are helping fund the data-gathering efforts and the technology's development.

The Pacific expedition, which will end in mid-September, will gather data that will be more extensive than what has been collected in the past 40 years, Slat said. It also will give a better estimate of the how much plastic waste is in the Pacific Ocean, he said.

The boaters are using GPS and a smartphone app to search for and record the plastic. They take samples and ship them to the Netherlands, where the plastics are counted and recorded.

An interesting finding has been that most of the plastic mass in the Pacific Ocean is large debris, Slat said.

"This shows us why it is urgent to do the cleanup because that debris will eventually be fragmented by ultraviolet radiation into smaller and smaller pieces that are more dangerous because they get ingested by birds and fish and they end up in the food chain," Slat said.

The Great Pacific Garbage Patch was discovered by Charles J. Moore in 1997 as he returned home from the Transpacific Yacht Race, which starts in Los Angeles and ends in Honolulu.

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