Microplastics in the
Great Lakes

The First Comprehensive Look

The earliest systematic survey of microplastics in all five Great Lakes was conducted in 2012–2013 by Marcus Eriksen, Sherri Mason, and colleagues at SUNY Fredonia and the 5 Gyres Institute. Sampling across a ~700-nautical-mile expedition, the researchers found microplastic particles at every single station — from the open lake surface to nearshore areas far from obvious urban sources.

The results, published in Marine Pollution Bulletin in 2013, were striking. The average concentration across sampled stations was approximately 43,000 microplastic particles per km². One station located downstream from two major urban centers contained over 466,000 particles per km² — greater than all other stations combined. At the time, Lake Erie's concentrations exceeded measurements from the Great Pacific Garbage Patch, making it among the most plastic-polluted bodies of water ever documented.

More than a decade of follow-up research has not revealed improvement. A comprehensive assessment by researchers at the University of Toronto and the International Institute for Sustainable Development, examining water samples collected from the Great Lakes over the past ten years, found that nearly 90% of samples exceeded concentrations linked to potential harm to wildlife. Recent reports describe the current contamination as the highest levels in recorded history.

Where It Comes From

University of Toronto microplastics researcher Chelsea Rochman has identified three dominant sources of microplastics in the Great Lakes environment:

• Tire wear rubber — Every vehicle on every road in the watershed continuously sheds particles. These wash into storm drains, travel through tributaries, and accumulate in the lakes. A 2016 USGS study led by Sherri Mason found microplastics in all 107 samples collected from 29 Great Lakes tributaries across six states — with fragments, films, and pellets positively correlated with urban land cover and runoff events.
• Textile microfibers — A single synthetic clothing item (polyester, nylon, acrylic) releases up to 700,000 plastic fibers per laundry cycle. Microfibers account for an estimated 70–90% of total microplastics in surface waters. At Lake Superior beaches, researchers found that nearly 95% of microplastics collected were polyester fibers — directly traceable to textile sources.
• Paint particles — Road markings, boat hull coatings, and architectural paint degrade and enter waterways through weathering, rain, and mechanical abrasion.

Additional sources include pre-production plastic pellets (nurdles) spilled during industrial transport, the breakdown of single-use plastic packaging, and atmospheric deposition — microplastics transported by wind and settling onto the lake surface. Wastewater treatment plants remove most microplastics but not all; the residual fraction discharged at scale represents a continuous, diffuse source.

In the Water You Drink

The Great Lakes are the primary source of drinking water for tens of millions of people in eight US states and two Canadian provinces. Multiple studies have found microplastics in treated municipal tap water drawn from these sources.

Research published in PLOS ONE by University of Minnesota scientist Mary Kosuth found microplastics in 81% of globally sampled tap water, including samples from communities on the Great Lakes. A companion study measured an average of approximately 1.6 particles per liter in Great Lakes tap water — and roughly 4 particles per liter in beer brewed with Great Lakes water.

The International Joint Commission's Great Lakes Science Advisory Board has recommended designating microplastics as a formal "contaminant of mutual concern" under the Great Lakes Water Quality Agreement — a step that would trigger coordinated US-Canada monitoring and public reporting requirements. As of mid-2025, that designation has not yet been made.

Impact on the Ecosystem

The Great Lakes ecosystem supports more than 3,500 species of plants and animals, 300,000 jobs, and one of the most significant concentrations of freshwater biodiversity in the world. Microplastics are now distributed throughout this system.

• Fish — A study of three Lake Michigan tributaries found microplastics in the digestive tracts of 85% of fish sampled (EWG, citing peer-reviewed data). Ingested particles can cause physical damage, false satiety, and reduced feeding behavior. Chelsea Rochman has conducted research on microplastics in the fillet tissue of fish from Lakes Ontario and Superior that humans consume.
• Invertebrates — Zooplankton, benthic invertebrates, and filter-feeders like mussels ingest microplastics, potentially affecting feeding efficiency and reproduction at the base of the food web.
• Waterbirds — Double-crested cormorants, ring-billed gulls, and other Great Lakes waterbirds have been found with microplastics in their digestive systems. The lakes support some of the largest freshwater bird populations in North America.
• Chemical vectors — Microplastics adsorb and concentrate persistent organic pollutants (PCBs, PAHs, DDT metabolites) that remain in Great Lakes sediments from legacy industrial contamination. Wildlife and humans ingesting plastic-bound contaminants may receive a more concentrated chemical dose than if those chemicals had simply been dissolved in the water.

The Human Health Question

Research on the human health implications of microplastic exposure is advancing rapidly but remains incomplete. Several findings are now well-established in the scientific literature:

Microplastics have been detected in human blood, lungs, brain tissue, placenta, and breast milk. Early evidence from laboratory and animal research links chronic exposure to inflammation, endocrine disruption, and potential effects on neurological function. Microplastics have been shown to cross the blood-brain barrier in animal models.

For Great Lakes region residents specifically, the primary exposure pathways are drinking water and fish consumption. People who regularly eat Great Lakes fish may ingest microplastics present in both the digestive tract and, in some species, in fillet tissue.

The National Toxicology Program completed a systematic review of microplastic health effects, finding sufficient evidence from animal studies of adverse effects at high concentrations. The NTP concluded that inadequate human data currently prevents firm conclusions about dose-response in real-world settings — a characterization that reflects the state of the science, not necessarily the absence of risk.

The Donna Kashian at Wayne State University, who researches Great Lakes toxicology, has stated there is "almost nothing untouched" by microplastics anymore — including the region's drinking water and food supply.