Marine litter is found on coasts, on the water surface, in the water column, on the seabed, even in the deep seas where it causes harm to marine ecosystems. Litter emissions come from diverse land-based or sea-based sources, such as urban areas, tourism, fisheries, shipping, aquaculture, agriculture and other activities.  As can be seen from the Map of the Week, while the percentages of different litter categories vary from one location to another, the category of litter that predominates is artificial polymer materials. It is estimated that more than 150 million tonnes of plastics have accumulated in the world's ocean, while 4.6-12.7 million tonnes (from Jambeck et.al) are added every year. 
Marine litter is one of the 11 descriptors monitored in the framework of the Marine Strategy Framework Directive which aims at achieving Good Environmental Status of European Union (EU) marine waters. The European Union is taking action on plastics through policies to tackle plastic pollution and marine litter, and to accelerate the transition to a circular plastics economy.
Many initiatives are undertaken to address marine litter that involve many different stakeholders. You could be involved too! Below are some examples.
It is broadly assumed that approximately 80% of marine litter is land-based, with regional fluctuations.  To address marine litter, it is thus essential to also address litter in rivers and to ensure waste prevention. The EU Action Plan: "Towards a Zero Pollution for Air, Water and Soil" includes several targets for 2030, including the improvement of water quality by reducing waste, plastic litter at sea (by 50%) and microplastics released into the environment (by 30%).
The data in this map are provided by EMODnet.