The majority of plastic in the Great Pacific Garbage Patch is discarded fishing gear.

[u/lnfinity]

[u/Farmer771122]

if you copy/paste his comment into google, the first result is this:

https://www.worldwildlife.org/stories/ghost-fishing-gear

which says

More than 12 million tons of plastic end up in our seas every year. Plastic pollution plagues every corner of the ocean and despite growing awareness, the problem is only getting worse. Fishing gear accounts for roughly 10% of that debris: between 500,000 to 1 million tons of fishing gear are discarded or lost in the ocean every year. Discarded nets, lines, and ropes now make up about 46% of the Great Pacific Garbage Patch.

So there's the source. He wasn't entirely accurate, but his sentiment is close.

[u/seaspirit331 → u/Farmer771122]

And if you do a basic Google Scholar search for plastics sources in the marine environment, you'll come across publications like this one

From the article "MPs are abundant in the Great Pacific Garbage Patch, with about 1.69 trillion (94%) floating pieces that are microplastics."

Later on in the same article "About 80% of plastic pieces in the ocean originated from the terrestrial environment"

[u/Kagrok → u/seaspirit331]

94% of the pieces are microplastics does not mean 94% of the mass are microplastics

If I had 1 piece of fish and some steamed rice on a plate you could say that 99% of the pieces of food on my plate are rice, and 50% of the food mass is fish.

it's not really intuitive but the Potato Paradox is even crazier