There are probably more tiny bits of plastic in the Yakima River than you’d expect. That’s according to a first-of-its-kind study.
Researchers at Central Washington University sampled nine spots on the Yakima River. Samples came from Snoqualmie Pass all the way to its mouth in the Tri-Cities. Not many studies like this previously had been done in rivers, said Clay Arango, a biological sciences professor at the University.
Every spot the researchers sampled – even near the headwaters – had plastic fibers. Most of the sample areas had 2.5 to 5 pieces per liter, Arango said.
“ Who would expect plastic up there? There's not much up there. Well, that was one of the higher amounts of plastic,” Arango said, at Cowiche Canyon Conservancy’s 2026 Winter Talk series in Yakima.
Using a bit of mathematical estimation, the researchers found more than 170,000 pieces of plastic flowing down the river every second.
“ So stand by the side of the river and count one Mississippi, and all the water that flowed past you has 171,000 pieces of plastic in it. Every second, every minute, every hour, every day,” Arango said.
The unpublished study is undergoing peer reviews. Arango advised master’s student J Shah on her thesis. Shah spoke about her research in a university news release last year.
“I really wanted to look at microplastic distribution in the Yakima River, and I was really interested in how microplastics were entering the aquatic food web,” Shah said in the release. “At the time, to the best of our knowledge, there wasn’t a study that did what we did.”
The study also found plastic fibers in the water column, on the riverbed, and inside the tiny insects many fish eat, including midges, caddisflies, stoneflies and mayflies.
“The point being here is that two-thirds of insects had fibers,” Arango said. “These are little tiny things and little tiny guts that's a lot of plastic in those guts.”
Plastics can bioaccumulate, or gradually build up substances, in the food chain.
“If the insects have plastic and the fish eat the insects, it's not too much of a leap of the imagination to think that we've got plastic moving all the way up through this food web into the fish that are really important for recreation and subsistence in our area,” Arango said.
However, he said, people all around the world are working to reduce microplastics, although it is a daunting task.
“Until we stop putting plastic down the drain and using it in consumer materials and throwing it on, it's going to happen forever, until essentially we run out of oil to make plastic out of right,” he said.
The final talk in the series will compare the effects of removing the Nelson Dam on the Naches River to other large dam removals. The talk will be 6 p.m. tonight at Yakima Valley College’s Kaminski Conference Center. It can also be streamed on the college’s YouTube channel.
Produced with assistance from the Public Media Journalists Association Editor Corps, funded by the Corporation for Public Broadcasting, a private corporation funded by the American people.