An environmental research group recently tested water from 50 river access sites at 32 water bodies throughout Montana for microplastic and found that, of those tested, more than half contained one or more types of the pollutant.

When plastic objects such as cups, bags and containers find their way to public lands, parks, rivers and lakes, they do not decompose but rather break down over time into smaller pieces known as microplastic. Although these pollutants are small — defined as being less than 5 millimeters in size — they can have a large impact, according to the Environment Montana Research & Policy Center, which conducted the study.

According to the study, birds and fish often mistake microplastic for food.

“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,” according to the report.

The goal of the study, released last week, was to examine the presence and type of microplastic near river access areas statewide. The 50 sites that were tested vary in physical geography, water-body type and how frequently they are used.

The center tested water at sites ranging from Miles City and Fort Peck all the way to Noxon and Yaak. The sites were tested for four different types of microplastic: fibers from synthetic fabrics and filaments such as fishing line, fragments from rigid plastics such as clear plastic containers, film from items like plastic bags and microbeads from personal care products like toothpaste.

At each site of the 50 sites, samplers walked out from the center of the river access ramp or trail to a water depth of approximately 2 feet and filled glass quart jars. When sampling in moving water, the jars were filled upstream from where the researchers had walked or were standing.

“We found plastics in waterways from every corner of the state, including some of our most remote rivers and lakes,” said Skye Borden, state director for the research and policy center.

About 66%, or 33 sites, contained one or more types of microplastic. Half of the sites contained fragments, 42% contained fibers and 18% contained film. Three fishing access sites — Upper Prickly Pear, Little Blackfoot and Flatiron Ridge — contained fibers, fragments and film.

Microbeads, which have been banned in personal care products in the United States since 2018, were not discovered at any of the sites.

In Northwest Montana specifically — from Seeley Lake to Thompson Falls and north — an interactive map of access sites tested shows the center looked at 13 areas. Of those 13, researchers discovered microplastic in six river access sites that are part of, or flow into, the following water bodies: Flathead Lake, Middle Thompson Lake, and the Tobacco, Kootenai, Clark Fork and Bull rivers.

At many of those water bodies, researchers pulled samples from several areas. At Flathead Lake, for example, researchers sampled water at access sites in Woods Bay on the east shore and Ducharme at the south end of the lake. Film particles were found at the Ducharme site, but the water at Woods Bay contained no microplastic.

In addition, the study also found that most of the sites with the highest microplastic concentrations were near metropolitan areas. The 10 most concentrated sites were within 40 miles of the center of one of Montana's seven core-based statistical areas, including Missoula, Butte and Billings.

The freshwater findings in Montana indicate microplastic is not just a threat to the world's oceans — a finding that has gained momentum in recent years as researchers flock to national and international shorelines to study the extent of the issue.

“Clearly, this report reaffirms that plastic pollution is not just a coastal problem,” Borden said. “It's a problem that we will need to address in the Northern Rockies as well.”

The report states that scientists are still documenting the scope of plastic pollution and “investigating its effects in freshwater ecosystems.” For example, researchers with the U.S. Geological Survey found microplastic in 90% of rainwater samples collected from six sites in and near the Rocky Mountain National Park.

In Montana, microplastic has been the subject of several studies in recent years.

One recent study found microplastic in 57% of samples collected from the Gallatin River watershed. According to the report, the United States Environmental Protection Agency is using the dataset in an assessment of “exposure and identification of microplastics in sediment, tissue, and wastewater, towards the designation of plastics as a pollutant.”

In 2018, researchers with the Flathead Lake Biological Station at Yellow Bay on Flathead Lake began collecting and analyzing water samples around the lake. In a 2019 update on the project that was posted to the station's website, researchers found that rivers retain more microplastic than previously thought. The research was spearheaded by visiting researcher Xiong Xiong, who conducted a similar project on Flathead Lake as he did on the Yangtze River — one of the largest rivers in the world that is believed to be the largest plastic-export river to the ocean. Findings from the Yangtze River study “indicate that river systems are at great risk for microplastic pollution,” among other discoveries.

Results from the similar study performed on Flathead Lake are still being compiled, but are expected to be released soon.

Reporter Kianna Gardner can be reached at 758-4407 or kgardner@dailyinterlake.com