(CNN) In June, Ben Lecomte set out on a boat from Hawaii to spend 80 days swimming through the world's largest collection of marine litter.
The 52-year old Frenchman, who has been based in the US since 1991, swam for up to eight hours at a time within the Great Pacific Garbage Patch. In total, he swam 300 nautical miles.
Also known as the Pacific trash vortex, the garbage spans an area between North America and Japan of roughly 1.6 million square kilometers -- three times the size of France, and more than double the size of Texas. It is bounded by an enormous gyre -- spinning oceanic currents that pull trash towards the center and trap it there, creating a garbage vortex.
Find out more about Call to Earth and the extraordinary people working for a more sustainable future
A recent survey estimates that at least 79,000 metric tons of plastic swirl around the patch. Between 10% and 20% of the debris is thought to have been swept out to sea by the Tohoku tsunami which struck the coast of Japan in 2011.
Some of the garbage biodegrades, but anything made of plastic does not. Instead, pummeled by waves and broken down by sunlight, it fragments into tiny pieces -- known as microplastics.
Lecomte says he expected to see big debris and was not surprised to encounter toothbrushes, plastic bags, children's beach toys, fishing nets, trash cans and laundry baskets bobbing around in the water. However, he says, he was startled by "the high concentration of microplastics," which has turned the once sparkling ocean into a cloudy plastic soup.
Lecomte says that most of the time the water is choppy and the microplastic is not visible from the surface. Instead, "it is pushed down in the water column to about 5 meters." From a swimmer's perspective, it's like "looking up at the skies on a snowy day -- but in reverse," he tells CNN.
Read: She filmed sharks for 'Jaws' -- then dedicated her life to protecting them
The swim wasn't dangerous: Lecomte was able to maneuver around bigger pieces of debris and wore a snorkel, so there was little chance of him swallowing microplastic. "The most unpleasant thing was facing this awful scene every day," he says.
The "Vortex swim" was not Lecomte's first extreme marine swim. In 1998, aged 31, he swam across the Atlantic from Cape Cod to France.
Read: A vast library of tree DNA could protect the world's forests
In December 2018, he attempted to set a world record by being the first person to swim the entire breadth of the Pacific Ocean, from Tokyo to San Francisco. After 1,500 nautical miles, the expedition was scuppered when storms irreparably damaged the mainsail of his support boat.
But his time in the Pacific inspired Lecomte to undertake a different mission. Appalled by the amount of trash he encountered on the high seas, he decided to dive into the garbage patch and share his swimmer's perspective with a global audience.
During the voyage, Lecomte and his crew of nine gathered detailed data on the plastic in the garbage patch.
Marine debris researcher Drew McWhirter led the scientific research on board. "I wanted to find out 'what does the garbage patch look like? What kinds of plastic are accumulating there,'" he says.
With direction from land-based scientists, the boat's crew attached floating GPS trackers to large pieces of debris, so their movements can be tracked.
The team also collected, and counted, more than 43,000 plastic fragments using a "manta trawl" net -- a fine-meshed oceanographic instrument designed to skim the surface of the water to collect samples. They towed the net for half an hour, twice a day, and then counted and analyzed the contents.
At the start of the journey, as the boat sailed away from Hawaii, "we were getting 40 to 80 pieces of plastic in a 30-minute tow," says McWhirter. "It was really easy to count."
But as the boat traveled further from land, the number of fragments climbed rapidly.
In early July, the boat "crossed an invisible border," says McWhirter. The water's surface looked the same but over three days, the plastic concentrations scooped by the net leaped from the hundreds to the thousands. "One day we hit 3,028 pieces of microplastic in a 30-minute net tow," says McWhirter.
By extrapolating the numbers, it's clear that "there are millions of pieces of microplastic in a square kilometer of ocean," says McWhirter. "There's so much plastic, it's hard to wrap your head around it."
The team also looked for plastic inside fish. Every time they caught one, they examined its gut contents and took a flesh sample -- before cooking and eating it.
Plastic fragments were not visible in most of the dissected fish, but one mahi mahi had a piece of plastic in its stomach that was macro -- not micro -- in size. "It was really disturbing," says McWhirter, "but we still ate it."
The crew sent samples of seawater and slices of fish flesh to Sarah-Jeanne Royer, a marine plastics expert at Scripps Institution of Oceanography and the expedition's lead scientist on dry land.
She is examining the samples for plastic microfibers -- microscopically small plastic threads that are a mounting cause for concern.
Read: Bringing back bison to restore America's lost prairie
"Most of our clothes nowadays are made out of different types of plastic including polyester, nylon, Lycra, polypropylene ... and they shed microfibers at all times," says Royer. When laundered, a standard, six-kilogram load of synthetic fiber clothing releases "about 700,000 microfibers," she says. Scattered into the air or flushed down water pipes, the fibers eventually reach the ocean via waterways.
According to the Ellen Macarthur Foundation, 60% of today's clothing is made of plastic-based textiles.
Although microfibers are a source of plastic in the ocean, "we don't know how much it accounts for in terms of total marine plastic pollution," says Royer.
Royer is analyzing the seawater samples to better understand the geographical distribution of microfibers, and is examining the fish flesh to see if microfibers are lurking there. She says it will take another six months to get the results.
"Finding microfibers would show that they are not always excreted by the fish but can pass through cell walls and get lodged in flesh," she says. Research on the impact of microfibers is in its infancy and "we don't know if that would have health consequences for people who eat the fish," she says.
It is hard to conceive of a way to remove microfibers from the ocean on a grand scale, says Royer, but she hopes that scientific data will prompt policymakers to legislate for technical fixes to prevent the fibers entering the ocean in the first place. She points to companies such as Filtrol that are developing filters that remove microfibers from washing machine outflows.
Awareness-raising is another priority. Ben Lecomte says his face-to-face experience with the Pacific's garbage has prompted him to reduce his consumption of plastic. He hopes that by revealing what's going on "below the surface" he can "inspire people to stop using single-use plastic and to rethink the way we live."