When Boyan Slat was 16, he went diving in Greece, and was shocked to see more plastic bags than fish. Seven years later, he’s raised more than $30 million to get rid of ocean plastic. Two-thirds of donations in the last few months came from Silicon Valley — including Peter Thiel, who granted Slat his prize for entrepreneurial college dropouts. What started as a high school science project is now a multimillion-dollar effort to launch what Slat promises will be “the largest cleanup in history,” as early as next year. But some scientists think it’s a fool’s errand that won’t come close to solving the problem.

Slat’s company, The Ocean Cleanup, wants to launch a fleet of floating trash collectors that will clean up to 50 percent of the great Pacific garbage patch in five years. That’s an area between Hawaii and California where plastic debris accumulates due to wind and ocean currents. But do we really need giant trash collectors in the open ocean? The science we have so far suggests the time and money could be better spent investing elsewhere, like in waste management or recycling, experts say.

“Cleaning up in the middle of the Pacific Ocean is, in my view, not a very clever way to address this problem,” says marine biologist Jan van Franeker of Wageningen Marine Research in the Netherlands. “It’s such a waste of energy.”

Nonetheless, investors have bought into the idea of a plastic-collecting flotilla. With the help of a viral TEDx Talk, Slat raised $2.2 million in crowdfunding from 40 countries, he says. Having spun that boost into even larger financial commitments from Silicon Valley, he knows exactly what his audience there wants. “It’s using technology to make the world a better place, which they all say they want to do,” Slat tells The Verge. “It’s a very exciting adventure.”

The project does sound futuristic: Slat’s cleanup system envisions a series of floating booms that will be anchored in a deep layer of ocean water, almost 2,000 feet deep, where currents are slower than at the surface. That means that floating plastic debris will move faster than the booms themselves, concentrating into a central area where ships would collect the trash once a month. As early as December, a 0.6- to 1.2-mile-long prototype could be deployed 50 to 100 miles off of San Francisco for about a month. To make money, Slat eventually plans to have companies like Apple or Microsoft sponsor individual booms, giving them access to live data on how much plastic they’re collecting for branding purposes. “It’s almost like a gamification of cleaning the ocean,” Slat says. The collected debris can then be recycled into pellets; Slat plans to sell those pellets to companies that can manufacture Ocean Cleanup-branded goods, such as the black and bright blue sun glasses he sports when he talks to the press.

There are a few holes in the project, according to scientists. First of all, we don’t really know where most of the plastic is in the ocean. In 2015, a Science paper estimated that around 8 million metric tons of plastic waste entered the ocean in 2010 from land. (To put that number in perspective, that’s “five grocery bags filled with plastic for every foot of coastline in the world,” the study author told Time.) In 2014, another study estimated that there’s about 270,000 tons of plastic debris floating in the ocean. That means that only 3 percent of plastic is floating at the surface. The rest is thought to either be at the bottom of the sea floor, suspended in the water column, eaten by marine animals, or washed up ashore in remote islands. Tiny pieces of plastic, called microplastics, can also be found in sediments and even frozen inside Arctic ice. “By focusing on the middle of the ocean, you’re missing the boat,” says Marcus Eriksen, the co-founder and research director at the nonprofit The 5 Gyres Institute.

Plastic waste sinks, shreds, and breaks down into microplastic before making it to the open ocean, Eriksen says. So while Slat’s booms in the great Pacific garbage patch will detect some plastic, most of it will be big pieces of debris like fishing nets, crates, and buoys, Eriksen says. That’s not the plastic debris that’s most harmful — the smaller pieces are. Sea turtles that eat plastic bags thinking it’s food can choke on them. Eating plastic can also give birds and fish a false sense of feeling full — so whenever the animal needs to birth a pup or withstand a storm, its belly full of plastic doesn’t provide enough energy to survive. Van Franeker says that in a small albatross species he studies, about 90 percent of birds have plastic in their stomachs.

Slat says that his team has conducted extensive research in the great Pacific garbage patch, sending some 30 vessels and even a plane to study how much plastic and what kind of plastic is there. The data collected during the expeditions hasn’t been peer reviewed or published yet, so Slat and Julia Reisser, an oceanographer with The Ocean Cleanup, couldn’t discuss it. But the number of large plastic objects observed in the garbage patch is definitely bigger than what was published in previous studies, Reisser says. “By being there, I can tell you it’s shocking,” she says. “There’s lots and lots of plastic.” Those large pieces need to be picked up before they turn into harmful small pieces, Slat says.

So, is there anything we can do to solve the plastic debris problem? First of all, people should just use less plastic — and be aware of the choices they make in their everyday lives. Second, we need better recycling systems, especially in developing countries in Southeast Asia where demand for plastic goods is increasing, but there’s no waste management system in place to keep that plastic from waterways. “If you think about it as an overflowing sink, the first thing you’re gonna do before cleaning up the water is to turn the faucet off,” says Sherry Lippiatt, the California Regional Coordinator for NOAA's Marine Debris Program. “That’s the only real long-term solution.”

Cleanups do have a role to play, but only if done where it makes sense, experts say. Most NGOs and government agencies agree that we have to work upstream, Eriksen says, mostly catching plastic in rivers before it enters the ocean. Otherwise, the debris is going to shred and sink to the bottom, where it’s unreachable. Projects like the Trash Wheel in Baltimore have been extremely successful at collecting over a million pounds of plastic trash before it leaves the harbor. The Ocean Conservancy is working with other partners to install similar systems in other rivers and lakes in several US cities, says Nick Mallos, the director of the Trash Free Seas Program at the Ocean Conservancy. (He wouldn’t say which ones.)

Slat says he’s not against prevention or cleaning up rivers. “It’s not either or,” he says. But the Ocean Cleanup’s niche, for now, is picking up plastic from the garbage patch, and its effort can complement all the other ones. In fact, he thinks his project can inspire people to recycle or use less plastic. “We are about to give people hope and I think hope makes people want to do something,” he says. “If you really think that the ocean will be polluted forever, there’s no way to make it go back to zero again, why bother?”