Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a lake, sea, ocean or waterway. Floating oceanic debris tends to accumulate at the centre of gyres and on coastlines, frequently washing aground, when it is known as beach litter or tidewrack. Deliberate disposal of wastes at sea is called ocean dumping. Naturally occurring debris, such as driftwood, are also present.
With the increasing use of plastic, human influence has become an issue as many types of plastics do not biodegrade. Waterborne plastic poses a serious threat to fish, seabirds, marine reptiles, and marine mammals, as well as to boats and coasts. Dumping, container spillages, litter washed into storm drains and waterways and wind-blown landfill waste all contribute to this problem.
Types of debris 
Researchers classify debris as either land- or ocean-based; in 1991, the United Nations Joint Group of Experts on the Scientific Aspects of Marine Pollution estimated that up to 80% of the pollution was land-based. A wide variety of anthropogenic artifacts can become marine debris; plastic bags, balloons, buoys, rope, medical waste, glass bottles and plastic bottles, cigarette lighters, beverage cans, polystyrene, lost fishing line and nets, and various wastes from cruise ships and oil rigs are among the items commonly found to have washed ashore. Six pack rings, in particular, are considered emblematic of the problem.
Eighty percent of marine debris is plastic. Plastics accumulate because they typically don't biodegrade as many other substances do. They photodegrade on exposure to sunlight, although they do so only under dry conditions, as water inhibits photolysis.
Ghost nets 
Fishing nets left or lost in the ocean by fishermen – ghost nets – can entangle fish, dolphins, sea turtles, sharks, dugongs, crocodiles, seabirds, crabs and other creatures. These nets restrict movement, causing starvation, laceration and infection, and, in animals that breathe air, suffocation.
Nurdles and plastic bags 
Nurdles, also known as "mermaids' tears", are plastic pellets, typically under five millimetres in diameter, that are a major component of marine debris. They are a raw material in plastics manufacturing, and enter the natural environment when spilled. Weathering produces ever smaller pieces. Nurdles strongly resemble fish eggs.
Plastic waste has reached all the world's oceans. This pollution harms an estimated 100,000 sea turtles and marine mammals and 1,000,000 sea creatures each year. Pelagic plastic pieces in the center of our ocean’s gyres outnumber live marine plankton, and are passed up the food chain to reach all marine life. Plastic shopping bags can clog digestive tracts when consumed and can cause starvation through restricting the movement of food, or by filling the stomach and tricking the animal into thinking it is full. A 1994 study of the seabed using trawl nets in the North-Western Mediterranean around the coasts of Spain, France and Italy reported mean concentrations of debris of 1,935 items per square kilometre. Plastic debris accounted for 77%, of which 93% was plastic bags.
Sources of debris 
An estimated 10,000 containers at sea each year are lost by container ships, usually during storms. One famous spillage occurred in the Pacific Ocean in 1992, when thousands of rubber ducks and other toys went overboard during a storm. The toys have since been found all over the world, providing a better understanding of ocean currents. Similar incidents have happened before, such as when Hansa Carrier dropped 21 containers (with one notably containing buoyant Nike shoes). In 2007, MSC Napoli beached in the English Channel, dropping hundreds of containers, most of which washed up on the Jurassic Coast, a World Heritage Site.
In Halifax Harbour, Nova Scotia 52% of items were generated by recreational use of an urban park, 14% from sewage disposal and only 7% from shipping and fishing activities. Around four fifths of oceanic debris is from rubbish blown onto the water from landfills, and urban runoff. In the 1987 Syringe Tide, medical waste washed ashore in New Jersey after having been blown from Fresh Kills Landfill. On the remote sub-Antarctic island of South Georgia, fishing-related debris, approximately 80% plastics, are responsible for the entanglement of large numbers of Antarctic fur seals.
Marine litter is even found on the floor of the Arctic ocean.
Great Pacific Garbage Patch 
Once waterborne, debris becomes mobile. Flotsam can be blown by the wind, or follow the flow of ocean currents, often ending up in the middle of oceanic gyres where currents are weakest. The Great Pacific Garbage Patch is one such example of this, comprising a vast region of the North Pacific Ocean rich with anthropogenic wastes. Estimated to be double the size of Texas, the area contains more than 3 million tons of plastic. The gyre contains approximately six pounds of plastic for every pound of plankton per cubic meter of seawater. The oceans may contain as much as one hundred million tons of plastic.
Islands situated within gyres frequently have coastlines flooded by waste that washes ashore; prime examples are Midway and Hawaii. Clean-up teams around the world patrol beaches to attack this environmental threat.
Environmental impact 
Many animals that live on or in the sea consume flotsam by mistake, as it often looks similar to their natural prey. Bulky plastic debris may become permanently lodged in the digestive tracts of these animals, blocking the passage of food and causing death through starvation or infection. Tiny floating plastic particles also resemble zooplankton, which can lead filter feeders to consume them and cause them to enter the ocean food chain. In samples taken from the North Pacific Gyre in 1999 by the Algalita Marine Research Foundation, the mass of plastic exceeded that of zooplankton by a factor of six.
Toxic additives used in plastic manufacturing can leach into their surroundings when exposed to water. Waterborne hydrophobic pollutants collect and magnify on the surface of plastic debris, thus making plastic more deadly in the ocean than it would be on land. Hydrophobic contaminants bioaccumulate in fatty tissues, biomagnifying up the food chain and pressuring apex predators. Some plastic additives disrupt the endocrine system when consumed; others can suppress the immune system or decrease reproductive rates.
Not all anthropogenic artifacts in the oceans are harmful. Iron and concrete typically do little damage to the environment as they generally sink to the bottom and become immobile, and can even provide scaffolding for artificial reefs. Ships and subway cars have been deliberately sunk for that purpose. Some organisms have adapted to live on floating plastic debris, allowing them to disperse all over the world and become invasive species in remote ecosystems.
Debris removal 
Techniques for collecting and removing marine (or riverine) debris include the use of specialized mechanical equipment designed to clean up floating debris such as a Trash Hunter. These debris skimmer boats easily retrieve a wide variety of manmade and organic floating debris from the waterway. Such activities are often undertaken regularly where floating debris poses danger to navigation. For example, the US Army Corps of Engineers reports removing 90 tons of "drifting material" from San Francisco Bay every month. The Corps has been doing this work since 1942, when a seaplane carrying Admiral Chester W. Nimitz collided with a piece of floating debris and sank, costing the life of its pilot. Once debris becomes "beach litter", collection by hand and specialized beach-cleaning machines  are used to gather the debris.
Elsewhere, "trash traps" are installed on small rivers to capture waterborne debris before it reaches the sea. For example, South Australia's Adelaide operates a number of such traps, known as "trash racks" or "gross pollutant traps" on the Torrens River, which flows (during the wet season) into Gulf St Vincent.
Laws and treaties 
Ocean dumping is controlled by international law, including:
- The London Convention (1972) – a United Nations agreement to control ocean dumping
- MARPOL 73/78 – a convention designed to minimize pollution of the seas, including dumping, oil and exhaust pollution
European law 
In 1972 and 1974, conventions were held in Oslo and Paris respectively, and resulted in the passing of the OSPAR Convention, an international treaty controlling marine pollution in the north-east Atlantic Ocean. The Barcelona Convention protects the Mediterranean Sea. The Water Framework Directive of 2000 is a European Union directive committing EU member states to free inland and coastal waters from human influence. In the United Kingdom, the Marine and Coastal Access Act is designed to "ensure clean healthy, safe, productive and biologically diverse oceans and seas, by putting in place better systems for delivering sustainable development of marine and coastal environment".
United States law 
In 1972, the United States Congress passed the Ocean Dumping Act, giving the Environmental Protection Agency power to monitor and regulate the dumping of sewage sludge, industrial waste, radioactive waste and biohazardous materials into the nation's territorial waters. The Act was amended sixteen years later to include medical wastes. It is illegal to dispose of any plastic in US waters.
Property law, admiralty law and the law of the sea may be of relevance when lost, mislaid, and abandoned property is found at sea. Salvage law rewards salvors for risking life and property to rescue the property of another from peril. On land the distinction between deliberate and accidental loss led to the concept of a "treasure trove". In the United Kingdom, shipwrecked goods should be reported to a Receiver of Wreck, and if identifiable, they should be returned to their rightful owner.
A large number of groups and individuals are active in preventing or educating about marine debris. For example, 5 Gyres is an organization aimed at reducing plastics pollution in the oceans, and was one of two organizations that recently researched the Great Pacific Garbage Patch. Heal the Bay is another organization, focusing on protecting California's Santa Monica Bay, by sponsoring Beach Cleanup programs along with other activities. Marina DeBris is an artist focusing most of her recent work on educating people about beach trash.
See also 
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|Wikimedia Commons has media related to: Marine debris|
- United Nations Environment Programme Marine Litter Publications
- UNEP Year Book 2011: Emerging Issues in Our Global Environment Plastic debris, pages 21–34. ISBN 978-92-807-3101-9.
- NOAA Marine Debris Program – US National Oceanic and Atmospheric Administration
- Marine Debris Abatement – US Environmental Protection Agency
- Marine Research, Education and Restoration – Algalita Marine Research Foundation
- Beach Litter – UK Marine Conservation Society
- Harmful Marine Debris – Australian Government
- The trash vortex – Greenpeace
- High Seas GhostNet Survey – US National Oceanic and Atmospheric Administration
- Social & Economic Costs of Marine Debris – NOAA Economics
- PSA Video: "Plastics Kill" by The Surfrider Foundation's Rise Above Plastics Program
- 25 years of debris collected | Visual.ly
- How the oceans can clean themselves – TED Talk