The Great Pacific Garbage Patch (also known a the Pacific Trash Vortex) was predicted back in 1988 by NOAA (National Oceanic Atmospheric Administration). Based on finding of high concentrations of marine debris accumulating in regions governed by ocean currents, they hypothesized that similar conditions would occur in other parts of the Pacific. Unfortunately, they were right.
It was found and reported in 1997, described as the "Eastern Garbage Patch" (EGP). It was implied that it was large chunks of visible debris, but it primarily consists of particles that are generally invisible to the naked eye.
pelagic debris, there is no "bright shining line" between the "normal" and "elevated" levels of pollutants to define the area. Never the less, the findings are alarming as we produce more indestructible trash each year.
Information on the photodegradation of plastics, the effects on wildlife, and the potential for reduction and cleanup are all at the Great Pacific Garbage Patch on Wikipedia.