Microplastics are pieces of plastic debris that are less than 5mm in size. Microplastics can come from larger pieces of plastic that have been degraded over time, or they can be manufactured for a specific purpose. Microplastic fibers come from clothes. Synthetic fabrics like nylon, polyester, and acrylic can be degraded into fibers.

Microbeads, which are tiny manufactured plastic particles commonly found in personal care and cleaning products. Microbead production has been banned in the United States since the passage of the Microbead-Free Waters Act in 2015. Microplastics from the atmosphere can also deposit in rivers.