In 2025, so much water stargrass grew in the Yakima River that crews could pluck out thousands of pounds in minutes.
“ We were able to pull out 2,000 pounds within two to three minutes last year at the Prosser Reach,” said Kristy Pentico, the education and outreach director with the Benton Conservation District.
The district has worked for nearly 20 years to slow the growth of water stargrass in the Yakima. It’s a native plant, but it’s choking the waterway and slows river flows, making it tough for salmon to move upstream.
The problem has gotten progressively worse over the years. It’s now taken over roughly 50 river miles on the Yakima.
“ It's natural to the river, but man, has it exploded beyond belief,” said Michael Crowder, who lives on the Yakima River and is retired from Barker Ranch in West Richland.
To help, a coalition has turned to mechanical harvesting and cutting. There’s simply too much stargrass to pull by hand. Last year, crews used several types of machines to remove stargrass.
Now, in several spots, the aggressive harvesting appears to have suppressed water stargrass, Pentico said.
Take Prosser Reach, where crews harvested thousands of pounds of stargrass.
“ We went back to the Prosser Reach this year, and we did not see much stargrass at all,” Pentico said. “We're thinking, coupled with the floods in December and our aggressive harvesting last year, we did see the suppression of the water stargrass in that area.”
So, the district applied for a one-time Department of Ecology Emergency Drought Funding award in collaboration with Yakima Basin Integrated Plan partners. This funding covered $618,000 in equipment purchase and $200,000 for one season of operation.
“We have worked hard to leverage how we do this with our partners to see what we can do if we scale up,” said Marcella Appel, Benton Conservation District manager.
Now, the district uses aquatic eco-harvesters, which pull the plants out by their roots, and weedoos, which use a sickle sidebar to chop down the plants.
“ (They’re) an entry tool. Think of getting your first tool kit, your wrenches, your screwdrivers. The things that we know,” Appel said.
Crews cut and harvested 15 river miles over 40 days between July 1 and Sept. 15.
Because the harvesters pull stargrass out by its roots, it’s a more permanent way to control the plant growth.
The weedoos allow crews to reach more shallow waters, but they work more like a lawn mower. That means the stargrass will grow back. Pentico said in some places, it appears to grow back slower than before.
In the future, the district plans to experiment with its timing: Do they chop a couple times in a season? Would an earlier chop work better than a later one?
All that chopped plant matter floats downstream. The extra biomass can propagate elsewhere, especially as it catches on other stargrass mats on the Columbia River, Appel said.
Some of that floating plant matter has also clogged irrigation canals, once shutting down the Columbia Irrigation District for 24 hours this year.
“ Which is not something we want to do,” Appel said at the September Yakima River Basin Water Enhancement Project workgroup meeting. “We are working on adaptive management as we're all learning our limits of both the cut and the drift and the timing with the screens.”
Crews are also trying to figure out what to do with all the plants they remove. The most likely solution could be composting, Appel said. Some irrigation districts place it on the banks, allowing it to dry out and blow away, said Curt Strifert, with the Columbia Irrigation District.
The hope is that one day, with so much stargrass removed, salmon will once again start spawning in this stretch of river.
A newly formed water stargrass coalition is developing a strategy plan that will look at additional ways to suppress water stargrass. That’s expected sometime next year, Appel said.
“One summer of cutting is a great start,” she said.
Read the audio transcript here.
