Volunteer citizen scientists collected water samples from Maryland sites along the Patapsco, Choptank, Nanticoke and Susquehanna rivers, as well as in the Chesapeake Bay itself near Talbot County. Laboratory researchers also analyzed samples from sites in Washington, D.C., Virginia, Pennsylvania and New York.

All of the sites contained plastic microfibers, 93% contained microfragments, 47% had microfilm and 27% had microbeads, the report found.

"Plastic pollution is pervasive, and it's a danger that's not just out there in some patch across the ocean. It's right here. It's knocking at our front door," Baltimore Harbor waterkeeper Alice Volpitta said during a news conference Tuesday along the Baltimore waterfront.

The groups unveiled the findings beside Mr. Trash Wheel, one of four anthropomorphized trash-collecting machines installed around the Baltimore Harbor by the city's Waterfront Partnership. In 2025 alone, the four wheels collected 768,000 pounds of garbage and debris from the city's waterways, said Allison Blood, senior manager of environmental projects and advocacy at the Waterfront Partnership.

"While that's an impressive accomplishment, we know that cleaning up the pollution downstream is not a long-term solution. We need to turn off the tap upstream," Blood said.

Microplastics are particularly difficult to capture because their small size — less than 5 millimeters, or about the size of a sesame seed — means they aren't easily collected by the wheels.

"Unlike an apple or piece of paper that will decompose gradually over time, plastic breaks down into smaller and smaller pieces of plastic," said Nina Harbison, an associate at Maryland PIRG, a sister organization to Environment America.

Once in the ecosystem, microplastics are often consumed by fish and other wildlife, causing a host of health problems. According to the National Oceanic and Atmospheric Administration, microplastics can attract and carry pollutants found in the water and release chemical pollutants of their own. Plastics and their associated chemicals can delay developmental stages, hinder reproduction and make it more difficult for animals to fight disease, the agency says.

Microplastics have also been found in the human body, and some studies have linked them to greater health risks. In one study of patients with plaque buildup in their arteries, those with microplastics in plaque had a higher risk of heart attack, stroke or death.

There is no "silver bullet solution" for addressing the "mini menace" of microplastics, Harbison said. But PIRG is among the groups that believe a bottle return system would go a long way in Maryland.

Maryland's "bottle bill" has been introduced repeatedly in the General Assembly. The current iteration has been introduced in each of the past four years but has yet to receive approval from the full House or Senate. Under the bill, plastic producers would contribute funds to operate the program, which would be overseen by the Maryland Department of Environment.

Environmental groups also point to other wins, including 2025's passage of broader "extended producer responsibility" in Maryland, requiring various packaging producers to pay fees that help cover the cost of recycling the materials.

In 2015, Maryland enacted a ban on "synthetic plastic microbeads" in personal care products and over-the-counter drugs. Beginning in 2020, the state banned most uses of polystyrene, also known by the brand name Styrofoam.

Since the polystyrene ban took effect, Baltimore's Waterfront Partnership has seen an 83% reduction in polystyrene collected by its trash wheels, Blood said. The partnership has also noted a 55% reduction in plastic bag pollution collected by the wheels after a local plastic bag ban.

"These reductions demonstrate that policies can prevent plastic pollution from reaching our waterways in the first place," Blood said.