The “garbage patches,” as referred to in the media, are areas of marine debris concentration in the North Pacific Ocean, circulated by the North Pacific gyre. The gyre spreads across the Pacific Ocean from Japan to the western U.S., and north-south from California to Hawaii. Its total size isn't well defined because there are numerous factors that affect the location, size, and strength of currents throughout the year, including seasonality and El Nino/La Nina.
Bits of floating plastic follow the currents, but most settle in calm areas in the center of gyres, shown above. The eastern patch lies within the area of the North Pacific Subtropical High, and the western patch is thought to be a small recirculation gyre off the coast of southern of Japan. Read about the ocean trash plaguing our seas.