Living in the United States, the Frenchman Ben Lecomte began the world's first swim across the Pacific ocean.
That's the term scientists use to describe billions of pieces of microplastic in the sea.
The swimmer is hoping to raise awareness of the plastic waste and ocean pollution blighting the water, with his support team hoping to carry out experiments throughout the trip, which is expected to take between six and eight months.
The mapped-out route will take Lecomte through the centre of the infamous Great Pacific garbage patch, or Pacific trash vortex, a giant gyre of marine debris the size of Texas.
Lecomte is shaking off any personal threat.
He will also wear a device to test levels of radioactive material from the Fukushima nuclear plant, which was hit by a tsunami in 2011.
"When I was little and I was with my father walking on the beach, I didn't see any plastic, or hardly any", he said. He will be accompanied throughout the journey by a support boat, where he will rest, eat and sleep before restarting his swim every morning.
In this picture taken on June 3, 2018, French swimmer Benoit "Ben" Lecomte poses during an interview with AFP in Choshi, Chiba prefecture.
'It made me think what (the) future for my kids is going to be like.
His team will collect water samples to learn more about the build-up of micro-plastics littering the area. Lecomte had previously swum across the Atlantic Ocean in 1998. This time, he says he has been practicing open-water swimming for hours every day to deal with the physical challenges, and "visualization and dissociation" to occupy his mind during the long hours of swimming.
"It didn't happen very soon after the Atlantic (swim) because I got married, I had children, so I put that aside".
To keep the boredom at bay, and to perhaps stave off thoughts of just how far he still has to go before he passes beneath the Golden Gate Bridge, Mr Lecomte draws up a detailed schedule of what he will think about for each of the eight to 10 hours he will spend in the water during the epic swim.