Marine debris, also called marine trash, is any human-made solid material that is disposed of or abandoned on beaches, in waterways that lead to the ocean, or in the ocean itself, regardless of whether disposal occurred directly, indirectly, intentionally or unintentionally. Dead seaweed, shells, carcasses or other naturally-produced materials are not included. 

  

Marine debris, including plastics, paper, wood, metal and other manufactured materials is found on beaches worldwide and at all depths of the ocean. About 60%-80% of all marine debris is composed of plastic and Ocean Conservancy's Trash Free Seas Alliance estimates that 8 million metric tons of plastic enters the ocean each year.

 

About 80% of marine debris originates from sources on land  and the other 20%, about 636,000 tons per year, comes from ocean vessels (US Department of Commerce 1999; Ramirez-Llodra et al. 2011). Cruise ships represent only 1% of marine vessels, but produce about 25% of ship-sourced waste; on average, a single cruise passenger produces 3.5 kg of waste per day. Read more....

 

http://www.oceanhealthindex.org/methodology/components/trash-pollution