Marine litter is any persistent, manufactured or processed solid material discarded, disposed of or abandoned in the marine and coastal environment.

Marine litter consists of items that have been made or used by people and deliberately discarded into the sea or rivers or on beaches; brought indirectly to the sea with rivers, sewage, storm water or winds; or accidentally lost, including material lost at sea in bad weather.

Marine litter originates from many sources and causes a wide spectrum of environmental, economic, safety, health and cultural impacts. The very slow rate of degradation of most marine litter items, mainly plastics, together with the continuously growing quantity of the litter and debris disposed, is leading to a gradual increase in marine litter found at sea and on the shores.

Thousands of pieces of trash are estimated to be afloat on every square mile of ocean.

Deficiencies in the implementation and enforcement of existing international, regional, national regulations and standards that could improve the situation, combined with a lack of awareness among main stakeholders and the general public, are other major reasons why the marine litter problem not only remains, but continues to increase worldwide. Furthermore, marine litter is part of the broader problem of waste management, which is becoming a major public health and environmental concern in many countries.

Around the world, the Regional Seas programmes are working to strengthen laws that prevent industries and individuals from dumping trash into oceans. It also works on capacity building to help national governments enforce these laws.