Plastic and more plastic…..
The Pacific Ocean Garbage patch stretches hundreds of miles across the North Pacific Ocean. The existence of a garbage patch was actually predicted by the National Oceanic and Atmospheric Association in 1988 after years of studying the amount of trash that was being dumped in the ocean. The garbage patch is not one solid mass of trash, but consists of countless tiny islands that come together in a vortex where many ocean currents meet. As the ocean currents and wind converge, they create a funnel that keeps the garbage together. These areas are called oceanic gyres.  The image below shows the Noth Pacific Gyre.
The Earth has 5 or 6 major oceanic gyres, which are huge spirals of seawater that are formed by converging currents. One of Earth’s larges gyres, the North Pacific Subtropical Gyre, fills most of the space between Japan and California.  Most of the trash collects several hundred miles north of Hawaii in an area called the North Pacific Subtropical Convergence Zone. This is where warm water from the South Pacific mixes with cooler water from the north. The area where the currents meet is called the convergence zone.  The convergence zone consists of 2 spinning eddies, the Eastern Garbage Patch and the Western Garbage Patch. These eddies combine to make the Great Pacific Garbage Patch. It can take trash several years to make it there, depending on where it is coming from. 
That trash that forms the garbage patch comes from many different sources. Eighty percent of the debris in the garbage patch comes from land (plastic bags, plastic bottles, other consumer goods). Another 10% is from abandoned fishing nets that are free floating in the ocean. The rest of the trash comes from recreational boaters, off shore oil rigs and large cargo ships. Cargo ships drop about 10,000 steel containers carrying computer monitors, resin pellets, plastic toys, etc. into the ocean each year.  Abandoned fishing nets are a huge problem. Many fishermen prefer plastic for their nets, as opposed to other materials because plastic is less expensive and highly durable. Bottom-set gill nets are especially dangerous to see life because they are buoyed by floats and anchored to the sea bottom, catching many different species of sea life in their grasp. 
Most of the garbage patch is made of plastic. Plastic in the ocean will last much longer than plastic on land because the plastic on land heats up much quicker and degrades. The plastic in the ocean is coated with algae in the cool ocean waters, which shields it from sunlight and keeps it from degrading as fast.  Over time, sunlight photo-degrades the plastic bonds and breaks the plastic into smaller pieces. This creates a much worse problem for vulnerable sea creatures who mistake these small pieces of plastic for fish eggs and other food products and ingest them. 
1. Moore, C.J., Moore, S.L., Weisberg, S.B., Lattin, G.L., Zellers, A.F. Algalita Marine Research Foundation and Southern California Coastal Water Research Project. (2002) A Comparison of Neustonic Plastic and Zooplankton Abundance in Southern California’s Coastal Waters. Marine Pollution Bulletin 44: 1035–1038.
2. McLendon, R. (2010) What is the Great Pacific Ocean Garbage Patch? MNN, Mother Nature Network. Available from: http://www.mnn.com/earth-matters/translating-uncle-sam/stories/what-is-the-great-pacific-ocean-garbage-patch. Accessed on: October 24, 2010.
3. Briney, A. (2010) Trash Islands of the Pacific and Atlantic Oceans. About.com. Available from: http://geography.about.com/od/globalproblemsandissues/a/trashislands.htm. Accessed on: October 22, 2010.