There are probably more tiny plastic debris in the Yakima River than you expected. This is a first-of-its-kind study.
Researchers from Central Washington University sampled nine sites in the Yakima River. Samples were taken from Snoqualmie Pass all the way to the mouth of the Tri-Cities. Clay Arango, a professor of biological sciences at the university, said this kind of research had not been done before in rivers.
Plastic fibers were present in every location the researchers sampled, even near the source. Arango said most sample areas detected between 2.5 and 5 pieces of debris per liter.
“Who would have thought there would be plastic in there? There’s not that much there. Well, that was one of the things that had a lot of plastic,” Arango said at the Kawich Canyon Conservancy’s 2026 Winter Talk Series in Yakima.
Using a little mathematical extrapolation, researchers found that more than 170,000 pieces of plastic flow through rivers every second.
“So stand on the edge of a river and count Mississippi by one. Every water that flows by you contains 171,000 pieces of plastic. Every second, every minute, every hour, every day,” Arango said.
This unpublished study has been peer-reviewed. Arango advised master’s student J. Shah on his thesis. Shah spoke about his research in a university news release last year.
“I really wanted to look at the distribution of microplastics in the Yakima River, and I was very interested in how microplastics enter the aquatic food web,” Shah said in the release. “At that time, to our knowledge, no study existed that did what we did.”
The study also found plastic fibers in the water column, riverbeds, and inside small insects that many fish eat, such as midges, midges, stoneflies, and mayflies.
“The important thing here is that two-thirds of the insects had fibers,” Arango says. “These are tiny little things, tiny little internal organs, and there’s a lot of plastic in those internal organs.”
Plastics can bioaccumulate, or accumulate material over time, in the food chain.
“If insects have plastic and fish eat those insects, it’s not a leap of the imagination to think that plastic is moving all the way through this food web into the fish that are really important to recreation and survival in our region,” Arango said.
But he said people around the world are working to reduce microplastics, albeit a daunting task.
“Unless we stop pouring plastic down the drain, using it in consumer products and throwing it away, this will continue forever until we essentially run out of oil to make plastic properly,” he said.
The final story in the series compares the impact of removing Nelson Dam on the Natchez River to the removal of other large dams. The talk will be held tonight at 6 p.m. at Yakima Valley College’s Kaminsky Conference Center. You can also stream it on the university’s YouTube channel.
Produced with the assistance of the Society of Public Media Journalists Editors Corps, funded by the Corporation for Public Broadcasting, a private corporation funded by the American people.
