Marine Debris; what is it and where does it come from? 

There are several definitions of marine debris from different sources that identify marine debris in differing degrees of detail. Each definition aims to describe the presence of unnatural matter in our oceans.

Simply put Marine Debris can be described as "garbage, trash, and litter that is in the water"^[3].

A more detailed description is that given by en.wikipedia.org;

"Marine debris usually applies to floating waste such as bottles, cans, styrofoam, cruise ship waste, offshore oil and gas exploration and production facilities pollution, and fishing paraphernalia from professional and recreational boaters. Marine debris is also called litter. It can enter the water directly through dumping into bodies of water or indirectly through runoff via rivers and streams. Marine debris threatens both marine life and coastal human habitations." ^{[1] [2]}

Under Key Threatening Processes in the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), “harmful marine debris” is defined as consisting of: “…land sourced plastic garbage, fishing gear from recreational and commercial fishing abandoned into the sea, and ship sourced, solid non biodegradable floating materials disposed of at sea.”

The International Oceanographic Commission (IOC) has identified marine debris, as one of the five major marine pollutants.

18,000 pieces of plastic litter are floating on every square kilometre of the world's oceans.

Six million tonnes of debris enters the world’s oceans every year.

More than half the debris in Australia’s seas comes from land—and up to 80 per cent around our cities.
Dr David Kemp, Minister for the Environment and Heritage March 2004 www.deh.gov.au/plasticdebris.

A 1997 study found that at least 267 species have been affected by marine debris worldwide, including 86% of all sea turtle species, 44% of all seabird species, and 43% of all marine mammal species, as well as numerous fish and crustaceans.
 Laist, D.W. “Impacts of Marine Debris: Entanglement of Marine Life in Marine Debris, Including a Comprehensive List of Species with Entanglement and Ingestion Records.” In Marine Debris: Sources, Impacts and Solutions, eds. J.M. Coe and D.B. Rogers. New York, NY: Springer-Verlag, 1997.