Marine litter is not a catch-all label. It refers to manufactured or processed solid material discarded, disposed of, or abandoned in marine environments (in the sea and along coastal areas). Most items start on land and move via runoff, rivers, wind, and losses at sea. Transport sorts materials by buoyancy, shape, and durability; therefore different fractions accumulate on beaches, float at the surface, remain suspended, or settle on the seabed. The core question—what counts as marine litter and what it is made of—drives prevention, interception, and recovery.

Definition

Marine litter is any persistent, manufactured or processed solid material—beyond plastics alone—that enters marine environments through direct loss or via waterways. Natural items (e.g., shells, driftwood) and liquids are excluded. Typical entries include packaging, consumer goods, industrial pellets, construction residues, and fishing gear. Consistent definitions make monitoring comparable across places and time, anchoring prevention strategies.

Materials

Plastics dominate by item count in most shoreline surveys due to high production, low density, and durability. Other materials recur: rubber (elastomer fragments, tires, gloves), metals (cans, wires, sheet pieces), glass/ceramics (bottles, shards), textiles (synthetic fabrics, ropes, nets; natural fibres when processed), processed wood and paper (treated timber, composites), and multilayer laminates and foams. The share shifts by setting: lightweight plastics crowd strandlines and surface waters; dense glass, metals, and some rubber accumulate on the seabed; textiles and fishing gear appear across compartments because fouling (organism growth) adds weight.

Sizes

Size controls transport and exposure and is usually classified into four categories:

• Macroplastics (> 25 mm): bottles, crates, bags, ropes, and nets; it drives entanglement and large-fauna ingestion.
• Mesoplastics (≈ 5–25 mm): typically originates from the breakage of larger objects.
• Microplastics (< 5 mm): arise as primary particles (pellets, microbeads, industrial powders) and as secondary fragments from mechanical stress, UV, and oxidation.
• Nanoplastics (< 1 µm): emerge from further weathering and require advanced analytical methods; their distribution remains poorly quantified.

Polymers

Some plastics are light and float, others sink. For example, polyethylene (PE) and polypropylene (PP) are the materials of bags, films and caps, and usually drift at the surface. PET bottles and PVC products are heavier; they may float if sealed but often end up sinking. Polystyrene (PS, including foams) breaks apart easily into many small pieces. Nylon and polyester, common in ropes, nets and clothing, release fibres and can either float or sink depending on conditions. Over time, all plastics change: chemicals used as additives can leak out, and roughened surfaces trap pollutants and metals, turning each fragment into a carrier for other substances.

Where it accumulates

Coasts. Beaches intercept floating and wind-blown items; strandlines accumulate lightweight packaging, cigarette filters, foams, and fishing fragments. Urban beaches show more single-use and sanitary items; rural stretches show more gear and bulky objects.

Surface and water column. Floating plastics and foams converge under wind and current features (fronts, ocean gyres). Fibres and denser fragments remain suspended, traveling with turbulence and river plumes.

Seabed. Dense materials and fouled plastics lodge in depressions and low-energy areas. Trawl surveys and imaging repeatedly trace cables, nets, pots, and bulky debris on continental shelves. Canyons and depositional basins store litter out of sight, complicating recovery.

Impacts

Composition sets exposure and impact. Nets, ropes, and loops impair movement, feeding, and breathing through entanglement; ghost gear keeps fishing. Films and foams mimic prey; hard fragments abrade digestive tracts; microplastics intercept in filter- and deposit-feeding species. Large objects smother benthic habitats; floating rafts transport invasive species. Fibres and fragments increase particle loads in sediments (layers of particles that settle on the seabed), altering oxygen exchange. These mechanisms justify action at source and along the pathway.

Marine litter persists because bulky objects sink and accumulate, while lightweight packaging and foams keep circulating until intercepted. Addressing both requires coordinated recovery at sea and interception along coasts. Ogyre contributes to this chain with context-specific actions: in Italy, Brazil and Indonesia, local fishers collect floating debris and ghost gear at the surface; in Senegal, waste fishers are divers who recover items that have already sunk to the seabed. Along coastal areas in Brazil and Indonesia, waste fishers intercept ocean-bound waste before it reaches marine environments, preventing new inputs. Certified cooperatives then take charge of the collected material, ensuring that it is sorted, recycled when possible, or otherwise disposed of in a responsible way. In this way, recovery closes the loop between collection and sustainable end-of-life.

A working classification links definition, material and size to fate and impact. Plastics dominate by numbers, but other materials such as metals, glass, rubber, textiles and composites also require attention. Recognising this broader composition keeps the focus on marine litter itself: a persistent mix of materials that demands coordinated monitoring, prevention and recovery across the full spectrum.

• European Environment Agency – EEA (2020), Plastics, the Circular Economy and Europe’s Environment – A Priority for Action link
• FAO (2021), Seabed Sources of Marine Litter link
• OECD (2022), Global Plastics Outlook link
• United Nations Environment Programme – UNEP (2024), Global Waste Management Outlook 2024 link
• United Nations Environment Programme – UNEP (2016), Marine Plastic Debris and Microplastics: Global Lessons and Research to Inspire Action and Guide Policy Change link
• WWF (2020), Stop Ghost Gear. The Most Deadly Form of Marine Plastic Debris link

👉 How big is global plastic waste today? link

👉 How does mismanagement fuel marine pollution? link

👉 How does plastic enter the Ocean? link

👉 How to classify micro and macroplastics? link

👉 Floating vs. seabed plastic: which is worse? link