Following Microplastics from Shore to Sanctuary

Febuary 10, 2026

Researchers in Monterey Bay National Marine Sanctuary are wrapping up a multi-year study, "From Watershed to Whales," to better understand how microplastics disperse, where they come from, and where they end up in marine ecosystems. The study also seeks to uncover how certain types of animals, including large whales, might be affected.

people in hats on a beach dump content from buckets into sieves
Filtering beach sand for microplastics at Salinas River State Beach in Monterey Bay National Marine Sanctuary. Photo: Chad King/NOAA

As debris in the environment travels down watersheds, microplastics are no exception. Microplastics are small plastic pieces or fibers that are less than 5 millimeters in size (smaller than a grain of rice), and can come from a variety of sources such as beauty product microbeads, textile plastic microfibers, and broken down from larger plastic pieces like beverage bottles, bags, and toys. They have been found on beaches around the world, even in our national marine sanctuaries, and have been documented in marine life and detected on the seafloor. Once they enter ocean waters, it can be difficult to understand where exactly these tiny plastics come from.

Since 2024, scientists and citizen science volunteers have collected samples at four different local beaches for detection and identification of microplastics within grains of surface sand (to about one inch deep), including Seabright, Zmudowski, Salinas River, and Carmel River state beaches. Sand samples were collected along 100 meter transects and within four random quadrat areas, filtered through 50 micron, 500 micron, and 5 millimeter sieves, and then preserved in jars for laboratory testing and analysis.

A man wearing a life jacket on a boat rinses contents from a fine-meshed sieve into a jar
While aboard the NOAA research vessel Tegula in Carmel Bay, sanctuary research ecologist Chad King rinses a sieve for possible detection and identification of microplastics filtered from surface ocean water. Photo: Amity Wood/NOAA

In addition, water sampling was conducted near the four river mouths, all of which drain into Monterey Bay National Marine Sanctuary. At each site, approximately 200 liters of surface ocean water was pumped through 50 micron and 500 micron sized sieves, and the remaining particle samples were collected and preserved for possible evidence of microplastics. For both beach and ocean water sampling, two size classes of microplastics were collected, particles between 50 and 500 microns, and particles between 500 microns and 5 millimeters. Larger particles are sorted and identified visually and with microscopes, while smaller particles are chemically analyzed using infrared spectroscopy, which determines their chemical signature by measuring how they scatter and absorb infrared light. The analysis could provide insight into inland microplastic sources and the relative contributions from local and global origins.

The field sampling will be completed February 2026, and study results will be shared with the state of California in late 2026. This work is being conducted with the California Marine Sanctuary Foundation, NOAA, Stanford University, and Moore Institute for Plastic Pollution Research, and is funded by the California Ocean Protection Council and California Sea Grant.

Stay tuned for future updates on this project, and in the meantime, explore resources to learn more about microplastics.

Amity Wood is the education and outreach coordinator for Monterey Bay National Marine Sanctuary