The Great Pacific Garbage Patch. Two "G"s and two "P"s. Nice symmetry there. The garbage patch presents nothing nice at all, but neither is it what many people expect. Most of it is not visible to the eye nor to satellite photography. Humanity is still the cause of it though.
Pelagic plastic is the official term. In an epic example of the Law of Unintended Consequences, I highly doubt (e.g.) Crest (just one brand name and by no means the only brand name; they are all included implicitly) ever even considered if the polishing particles they add to their toothpaste would ever be linked to the demise of the oceans and possibly, humanity. It turns out that I picked a relevant brand. Please click over and read the above Crest link. To their credit, Crest is phasing out plastic microbeads (aka polishing particles).
Also equally interesting that water treatment, filtration systems, sewage treatment methods and equipment, etc., were all largely designed prior to the advent of yet more evolution in our culture that would unleash a torrent of waste products that all our systems were not designed to handle. To be clear, the polishing particles in toothpaste, are spit down the drain. That goes to a water treatment plant where municipal sewage is cleaned up, including by filtration. The end product, newly clean water, is then discharged. Somewhere. If the plant is on the coast, there's a pipe that takes this out a couple miles in the ocean and "dumps it", although it is fairly clean to the eye. Except for all those polishing particles that are so small they slip right on through and go out as part of the clean water.
Finally inquiring minds may want to know the meaning of gyre. In a bit of further symmetry, the North Pacific gyre is basically the physical entity responsible for hoovering up all this garbage and aggregating it in one part of the Pacific.
Humanity. Who would have ever thought that a good thing like personal hygiene, could lead to a garbage patch of unknown size in the Pacific Ocean. That truth sure does seem to be stranger than fiction.