Plastic makes up at least 85% of all trash in the ocean, but it’s far from the only material polluting marine environments. Metals, rubber, textiles, glass, paper, abandoned fishing gear, and even hazardous chemical waste all end up in the sea. About 80% of this debris originates on land, washing into the ocean through rivers, storm drains, and coastal runoff, while the remaining 20% comes from maritime activities like shipping, fishing, and offshore drilling.
Plastic: The Dominant Material
Plastic is so prevalent in the ocean that it essentially defines the marine debris problem. Cigarette butts, plastic bags, food wrappers, bottles, and packaging film are among the most commonly found items. These materials are lightweight, durable, and produced in enormous quantities, which is exactly why they accumulate so effectively in marine environments. A plastic bottle takes an estimated 450 years to break down. Monofilament fishing line takes roughly 600 years.
What makes plastic particularly tricky is that it doesn’t truly decompose. Instead, it fragments into progressively smaller pieces. Particles smaller than 5 millimeters are classified as microplastics, and those under 100 micrometers (invisible to the naked eye) dominate the ocean by sheer count. These tiny fragments come from larger items breaking apart, but also from synthetic clothing fibers, tire dust, and cosmetic products that wash directly into waterways. By particle count, microplastics vastly outnumber all visible debris in the ocean.
Abandoned Fishing Gear
Lost and discarded fishing equipment is one of the most destructive categories of ocean trash. Nets, longlines, traps, and hooks continue catching and killing marine life long after they’re abandoned, a phenomenon known as ghost fishing. A study published in Science Advances estimated that nearly 2% of all fishing gear used worldwide is lost to the ocean each year. That translates to roughly 2,963 square kilometers of gillnets, over 75,000 square kilometers of purse seine nets, more than 739,000 kilometers of longline mainlines, and over 25 million pots and traps entering the sea annually.
Trawl nets have the highest loss rate at about 3.6% per year, followed closely by longline mainlines at 3.3%. These numbers may sound small as percentages, but the global fishing industry operates at such a massive scale that even a few percent adds up to an extraordinary volume of gear drifting through the ocean. In garbage patches and along coastlines, large tangled masses of netting are some of the most visible and damaging debris found.
Metals, Glass, Rubber, and Textiles
While plastic dominates, the ocean also collects aluminum cans, steel containers, glass bottles, rubber tires, and fabric. Metals corrode relatively faster than plastics in saltwater, but they can leach harmful compounds as they break down. Glass is essentially inert and can persist on the seafloor indefinitely, though it doesn’t pose the same ingestion risk to wildlife as plastic. Rubber, particularly from tires, contributes both visible debris and microparticles that wash off roads and into storm drains. Textiles, from lost cargo and discarded clothing to synthetic fabric fibers shed during laundry, add another persistent layer of pollution.
Hazardous and Industrial Waste
The ocean floor holds a legacy of intentional dumping that most people don’t think about. Off the coast of Southern California, for instance, the EPA has investigated disposal sites where companies dumped refinery waste, chemical waste, oil drilling waste, military explosives, and even radioactive materials for decades. One well-documented case involved acid waste containing DDT, a toxic pesticide, being loaded onto barges at the Port of Los Angeles and dumped directly into the Pacific. Industrial runoff, agricultural chemicals, and untreated sewage continue to flow into the ocean from land-based sources worldwide, adding invisible but harmful contamination on top of the physical debris.
Where It Accumulates
Ocean currents concentrate floating debris into large zones often called garbage patches. The Great Pacific Garbage Patch, the most well-known example, contains everything from large abandoned fishing nets to microplastics too small to see. Despite its name, it’s not a solid island of trash. You could sail through parts of it without noticing anything unusual, because much of the debris consists of tiny suspended particles rather than visible objects.
Perhaps more surprising is where most ocean trash actually ends up. An estimated 70% of plastic debris sinks to the seafloor rather than floating at the surface. Research in European seas found that litter densities on the seabed were consistently higher than at the surface. In the Mediterranean, seafloor litter density ranged from 0.4 to 48 items per hectare, compared to just 0.021 floating items per hectare at the surface. Debris sinks when it becomes waterlogged, weighted down by sediment, or colonized by marine organisms. This means the visible trash floating on the surface represents only a fraction of what’s actually in the ocean.
How It Gets There
Rivers are the primary conveyor belt for land-based trash reaching the sea. One study estimated that rivers collectively carry between 0.47 and 2.75 million metric tons of plastic into the ocean each year. Ten rivers alone account for roughly 93% of that river-borne plastic: the Yangtze, Yellow, Hai, Pearl, Amur, Mekong, Indus, and Ganges Delta in Asia, plus the Niger and Nile in Africa. The Yangtze is the single largest contributor, delivering up to an estimated 1.5 million metric tons of plastic waste into the Yellow Sea annually. These rivers pass through densely populated regions with limited waste management infrastructure, which is why such a large share of ocean plastic traces back to a relatively small number of waterways.
Beyond rivers, trash enters the ocean through coastal littering, storm drains, illegal dumping, and wind. On the maritime side, cargo ships lose containers overboard, fishing vessels shed gear, and offshore platforms generate waste. The combined result is a continuous flow of material into an environment where almost nothing breaks down quickly and currents carry debris thousands of miles from its origin.