Every year, millions of tons of plastic end up in the world's oceans. Much of it doesn't start at the beach. It starts in cities, sometimes hundreds of kilometers from the sea.
A plastic wrapper dropped on a street can be washed into a storm drain by rain. Storm drains often lead straight to rivers, and rivers flow to the ocean. Along the way, nobody filters the water, so the wrapper travels with it.
Once in the ocean, plastic does not rot like a leaf or an apple core. Instead, sunlight and waves break it into smaller and smaller pieces. Pieces smaller than five millimeters are called microplastics. Fish and seabirds can mistake them for food.
Some cities now put nets over storm drains, and some rivers use floating barriers to catch trash before it reaches the sea. Scientists say the most effective solution is simpler: use less single-use plastic in the first place, so there is less to catch.