Marine debris is litter that ends up in oceans, seas, or other large bodies of water.

This artificial debris gets into the water in many ways. People often leave trash on beaches or throw it into the water from boats or offshore facilities, such as oil rigs. Sometimes, litter makes its way into the ocean from land. This debris is carried by storm drains, canals, or rivers. The wind can even blow trash from landfills and other areas into the water. Storms and accidents at sea can cause ships to sink or to lose cargo.

Types of Debris
Any kind of trash can get into the ocean—from glass bottles to aluminum cans to medical waste. The vast majority of marine debris, however, is plastic.

Plastic products can be very harmful to marine life. For instance, loggerhead sea turtles often mistake plastic bags for jellyfish, their favorite food. And many sea animals and birds have become strangled by the plastic rings used to hold six-packs of soda together.

Plastics do not biodegrade quickly. Ironically, some new biodegradable plastics might not break down in oceans at all. These products are designed to break down when they heat up in a landfill or compost pile. Cooler ocean temperatures prevent these products from truly degrading.

Instead, like many other types of plastic, they simply break down into tiny particles called microplastics. Microplastics are pieces of debris between 0.3 and five millimeters (0.01 to 0.20 inches) thick, no thicker than a grain of rice. One example of microplastics is “nurdles,” the artificial pellets of raw material used in making plastic products. These tiny pieces of plastic can collect in the stomachs of marine animals, interfering with digestion. When marine animals ingest nurdles, they can feel “full” although they are not getting nutrients. The animals are at risk of malnutrition and starvation.

Floating on the ocean’s surface, nurdles and other small plastic pieces can block the sun’s rays from reaching plants and algae that depend on the sun to create nutrients. When these organisms are threatened, the entire marine food web may be disturbed.

As plastics get smaller and smaller, they release chemicals. One of those chemicals can be bisphenol A (BPA). Bisphenol A can interfere with animals’ reproductive systems. Fish are especially at risk when exposed to bisphenol A. Exposed fish produce fewer healthy offspring.

Bisphenol A and other chemicals build up in the fish’s body through a process called bioaccumulation. Plants or algae may absorb bisphenol A through the water. A fish, already exposed to the chemical, ingests more bisphenol A when it eats the algae. Top predators such as sharks or dolphins, which eat the fish, accumulate the most chemicals.

A reduction in the fish population can impact human activity in the area. Fisheries shrink, weakening the area’s economy. Fish that are harvested may have a high amount of toxins or other marine debris in their system as a result of bioaccumulation. Some of these toxins, such as mercury or bisphenol A, may be harmful to people, putting consumers at risk.

Another type of marine debris that is harmful to sea life comes from fishing gear. Discarded fishing lines and nets don’t stop fishing once humans are done with them. They continue to trap fish, along with marine mammals, turtles, and birds.

The Widening Gyre
Marine debris tends to collect in areas called ocean gyres. A gyre is a circular ocean current formed by Earth’s wind patterns and the forces created by the rotation of the planet. The area in the center of a gyre tends to be very calm and stable. The circular motion of the gyre draws in debris. The garbage makes its way into the center of the gyre, where it becomes trapped and builds up.

Trash buildups in the middle of gyres are known as garbage patches. For example, the Great Pacific Garbage Patch exists in the North Pacific between the U.S. states of California and Hawai'i. There is a similar patch in the North Atlantic.

For many people, the idea of a “garbage patch” conjures up images of an island of trash floating on the ocean. In reality, these patches are usually made up of microplastics that can’t always be seen by the naked eye. Satellite imagery of the oceans do not reveal a giant patch of garbage. Even so, scientists have found up to 750,000 bits of plastic in a single square kilometer (or 1.9 million bits per square mile) in the Great Pacific Garbage Patch. They have found more then 200,000 pieces of trash per square kilometer (520,000 bits per square mile) in areas of the Atlantic garbage patch.

No one knows exactly how much marine debris is in the oceans. Ocean gyres are too vast for scientists or volunteers to trawl the entire surface scooping up trash. In addition, not all of the trash floats. Denser debris can sink to the middle or bottom of the water. We have no way to measure this unseen marine debris.

What We Can Do About Marine Debris
Cleaning up marine debris is not as easy as it sounds. Many pieces of debris are the same size as small sea animals, so nets designed to scoop up trash would catch these creatures as well. Even if we could design nets that would just catch garbage, the size of the oceans makes this job too time-consuming to consider. And no one can reach trash that has sunk to the ocean floor.

Because of these difficulties, most environmentalists focus on preventing more garbage from entering the oceans. Since people became aware of the problem, governments and international organizations have passed laws against ocean dumping to try to reduce marine debris.

Many organizations, like the National Geographic Society, are working to educate people about the dangers of littering oceans. Through the Mission Blue program, National Geographic is working with other organizations, such as the Ocean Conservancy and Sea Web, to educate the public about threats to the ocean.

National Geographic Emerging Explorer David de Rothschild often collaborates with the Algalita Marine Research Foundation. Algalita’s founder, Charles Moore, discovered the Great Pacific Garbage Patch while sailing from Hawai'i to California. De Rothschild’s organization, Adventure Ecology, and Algalita both work to reduce the amount of marine debris, especially plastics.

Everyone can help reduce the problem. The most important rule—don’t litter! Don’t leave trash on the beach, toss it from a boat, or litter anywhere else. Remember, even trash dumped on land can make its way into bodies of water. In addition, remember to reduce, reuse, and recycle. The less trash we produce, the less that will end up in the ecosystem.