Microplastic in Montana

A Study of Fifty River Access Sites

We tested fifty river access sites across Montana this summer. Most of them had plastic in the water. 


Every day, people throw away tons of plastic “stuff” — cups, plates, bags, containers, forks, knives, spoons and more. All of this waste not only trashes our parks and public lands, but it also washes into our rivers, where it harms wildlife.

Once in our environment, plastic does not decompose. Instead, it breaks down into smaller and smaller pieces known as microplastics. 

For a bird or fish, it’s easy to mistake these small pieces of plastic for food — especially when there are thousands of pieces of microplastic floating in the waterway. Scientists have found that ingesting even tiny particles of plastic can alter the behavior and metabolism of fish in our lakes and rivers – and people can ingest these chemicals as they make their way up the food chain. 

Our Research

This summer, we tested the water at fifty river access sites across Montana for microplastics. We picked test sites that represented a wide range of physical geography, population pressures, and waterbody types. 

The plastics we found under the microscope were divided into four categories: 

  • Fibers from synthetic fabrics and filaments, such as fishing line and bailing twine;
  • Fragments from rigid plastics, including polystyrene and clear plastic containers;
  • Film from plastic bags and food wrappers; and
  • Microbeads from older personal care products.

Digital microscope images (clockwise from top left): a polystyrene fragment from the Blackfoot River; a red fiber from the Tobacco River; another fragment from Middle Thompson Lake; and a piece of film from the Yellowstone River.


Of the fifty sites tested, thirty-three (66%) contained one or more types of microplastic. 

Half (50%) of the sites contained microplastic fragments; twenty-one (42%) of the sites contained fibers; and nine (18%) of the sites contained film. Microbeads were not found at any site.

Click here to view an interactive map of our test results