Spring runoff may drive microplastic surges in Western rivers, study finds

KUNR Public Radio | By Kaleb Roedel

Published October 5, 2026 at 1:57 PM MDT

The Truckee River flowing high between tree-lined banks, with snow-covered mountains visible in the distance beneath a partly cloudy sky. — The Truckee River flows during spring runoff. A new study found microplastic concentrations in the river were nearly 10 times higher during high spring flows than during low fall flows.

Microplastic concentrations in Nevada’s Truckee River increased nearly tenfold during spring runoff, according to new research that offers a glimpse into how plastic pollution moves through some western waterways.

Researchers with the Desert Research Institute sampled the river, which flows from Lake Tahoe through Reno and eventually to Pyramid Lake, during low flows in fall 2022 and again during unusually high spring flows in 2023.

On average, they detected 0.4 microplastic particles per liter in the fall and 3.7 per liter in the spring. Monica Arienzo, who leads DRI’s Microplastics and Environmental Chemistry Lab, illustrates the seasonal difference with a quart-sized mason jar.

“If you take one of those quart mason jars and you dipped that in the Truckee River, the max amount of microplastics we found was one particle per mason jar,” Arienzo said. “While in the spring, the max we found was 10 plastic particles per one of those mason jars.”

Side-by-side illustration of a river in fall and spring. The spring river is higher and wider, with more microplastic particles shown moving through the water and along the riverbed. — A graphic illustrates how higher spring flows can mobilize microplastics that accumulate along riverbanks and in river sediments during lower-flow periods.

Hannah Lukasik led the research while seeking her master’s degree at DRI and the University of Nevada, Reno. She said plastic particles can build up on riverbanks and surrounding landscapes during drier months, and the spring runoff can mobilize them.

“I think a big contributor would be the re-wetting of the riverbank and the resuspension of the particles, which happens during those high flow events,” she said.

The study helps fill a research gap on microplastics in arid river systems, where flows can vary dramatically throughout the year, Arienzo said.

Previous studies of rivers in Colorado and Montana have measured microplastic concentrations comparable to those found in the Truckee. But the new research highlights how much concentrations can change depending on river conditions — something the authors say water managers and researchers should consider when deciding when to sample.

The most common plastics detected were PET, polypropylene and polyethylene; materials commonly used in consumer products. Researchers said the mix points to larger plastic items and single-use plastics as likely sources.

Arienzo said that better understanding when and where microplastic concentrations are highest could eventually help water managers find ways to prevent litter from reaching waterways.

This story was produced by the Mountain West News Bureau, a collaboration between Boise State Public Radio, Wyoming Public Media, Nevada Public Radio, KUNR in Nevada, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio and KJZZ in Arizona as well as NPR, with support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.