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Like Goldilocks, salmon like temperatures that are just so. Rivers that are too hot just won’t do.
When adult spawners make a left turn into the Yakima River each summer, the water they encounter can be too hot for them to survive. The lower Yakima is a huge bottleneck for adult and young salmon alike, said Zac Zacavish, a fish research biologist with the Yakama Nation.
“ In June to July, we have a super hot river. Water's coming down, temperatures are going up,” Zacavish said.
But there’s one small spot that could provide some relief and a bigger cold water haven for fish.
In the Tri-Cities, an irrigation return flow, called Amon Creek, is an anomaly on the lower Yakima. Studies show Amon Creek’s temperatures run roughly 4 to 18 degrees Fahrenheit cooler than the Yakima in the summer months.
“When you have something cold coming into a hot river, the fish are gonna find it, and ideally use it,” Zacavish said.
Biologists want to enhance Amon Creek’s cold water habitat. The work requires rerouting the creek, building a berm to direct cold water spilling into the Yakima and growing more native plants along the banks.
“We are creating, essentially, rest stops for (salmon) as they are migrating,” said Marcella Appel, Benton Conservation District manager. “Our hope is that the cold water refuge can increase some of our summer run populations.”
The large-scale restoration project has been years in the making. It’s a pilot project for the Yakima River, but it could one day serve as a guide for other cold water refuges upstream. That will be especially important as climate change contributes to warming waters.
The more work done on the lower Yakima River, the more fish that will return to their natal spawning grounds, Zacavish said.
Amon Creek used to run straight and narrow through this area, known as the Yakima River Delta habitat management unit, which is owned by the U.S. Army Corps of Engineers.
“We get a lot of birdwatchers, hikers, and dog walkers. Just about everybody that wants to get outdoors and not go too far come here,” said Brett Forge, a wildlife biologist with the Corps’ Walla Walla District.
Getting this project off the ground has taken more than eight years, Forge said.
Walking through the construction zone, Zacavish pointed out the former path it took, running through a culvert that used to be surrounded by invasive Russian olive trees.
Crews have now capped the old stream flow so that the water reroutes to a longer, meandering creek. They’ve extended the creek length from 700 to 1,400 feet, a much more natural flow, he said.
“ When you think of degradation, it didn't happen overnight,” Zacavish said. “It was a lot of earth-moving, a lot of things had to happen to get the system in the place that it's in. So it takes a lot to force it back into a state that is good for the fish.”
Adding bends back into a waterway can provide more habitat and reduce erosion, like crews did at Mecham Creek in Oregon.
For Amon Creek, that comes in the form of moving 30,000 cubic yards of earth, Zacavisch said. All the work they’ve done has also cost less than they’d initially expected, likely clocking in at just over $1 million.
One of the biggest pieces of the project includes building a berm that should create a pocket of cool, deep water.
Like a sandbar, the berm curves out from the bank roughly 70 feet, following the Yakima River flow. It’ll help deflect warmer water away from this additional cool water habitat, said Jaron Brown, a senior hydraulic engineer with Northwest Hydraulic Consultants. Brown is working on the Amon Creek design.
“Without the deflector, the cold water just mixes and disappears really fast into the river,” Brown said.
A similar project
This berm is the next generation of a similar project on the Pend Oreille River. Both rivers are tributaries of the Columbia River and contain important fish habitat.
In 2022, engineers built a berm along the Pend Oreille River, similar to what they’re building at Amon Creek. The goal on the Pend Oreille was to improve cold water habitat for bull trout.
One berm crews built is at the mouth of Indian Creek, near the Washington-Idaho border.
Following construction, thermal imaging showed a “ very distinct mixing zone” of the cold and hot water, said Jeremy Payne, a senior hydraulic engineer with Northwest Hydraulic Consultants. He worked on the Pend Oreille project. Thermal imaging shows cold water habitat has increased. A study of the area is awaiting publication.
The team has continued to monitor the cold water refuges at Indian Creek, Payne said. And they’ve figured out a few lessons from their initial construction.
For one, it seems the trout they’ve captured live in the cold water and find food in the warm water.
“ So we built all this cold water area, and we find that the area that they're using the most is actually on this thin boundary, where we don't have a lot of structure and wood, and we don't have a lot of cover,” Payne said.
This upcoming summer, he said, the team plans to build in more cover and habitat in that mixing zone. They’re going to put a lot more wood habitat in the berm, where much of the cold water pools. Crews will also dig a deeper pool where the cold water collects, he said.
Continuous monitoring and adaptive management strategies have helped engineers improve the designs on the Pend Oreille River, he said.
And while they’ve seen many trout using the cold water refuge on Indian Creek, biologists have yet to spot bull trout. It will take more long-term monitoring to see if bull trout return to this area, Payne said.
“(It was like), ‘Oh, we’re going to build this and they're all gonna come immediately,’” Payne said. “And it's like, ‘Maybe they're not.’ Is it we need to add a little more structure, we need a little more depth, or maybe just four years in a restoration context is still very new?”
The lessons learned and data they’ve collected over the past four years helped inform the design at Amon Creek.
“ It's really these first projects that (Northwest Hydraulic Consultants) got going, which we're building on now,” Appel said, of the Amon Creek construction.
Engineers at Northwest Hydraulic Consultants also built to-scale models to test their designs, Brown said.
“The physics in the model are the same thing as the physics in real life,” Brown said.
The model helped them figure out where to build the Amon Creek berm so that the deep water doesn’t fill up with sediment, he said. Floods in December 2025 likely pushed sediment downstream, which resulted in crews needing to add even more rock to get the berm to its correct level, Brown said.
At the construction site, crews add rocks to the berm. They’re designed to withstand river flows and stay in place.
Piles of dirt and rock now cover the site. It’s a bit like a home remodel, Appel said. They’re still in the building phase, but soon they’ll begin to add in the “decorations,” like cottonwoods and willow trees. The native plants will provide shade and create habitat for other wildlife.
An ongoing process
In fact, some wildlife is already returning to the area.
“ When we did the first clearing out of the Russian olives, we saw some wonderful animals and critters move back in,” she said. “One of the coyote pups loved working alongside our folks that were treating the Russian olives and would run alongside their dog.”
After planting the native plants this fall, it will take about three years for them to fully take hold.
“In two years it'll be at eye level, and then after that it's going to be taller. So instead of combating Russian olive, you have a little oasis of native vegetation,” Zacavish said.
The area will still require maintenance and upkeep, Appel said, which means more funding and community support.
Biologists plan to monitor with PIT tag arrays, microchips that help track fish, at the end of the berm and the mouth of Amon Creek. That will help them see if salmon use the “rest stop” or not.
But Zacavish thinks they could see fish in Amon Creek soon.
As the team walked out of the construction zone, they took a peek at the newly rerouted creekbed. To their surprise, the river had naturally started to reveal good spawning habitat.
“Oh my gosh,” Appel exclaimed, looking down at the riverbed, full of shining river rocks. “They’re beautiful.”
Before, Amon Creek was full of sediment, Zacavish said. He walked over to an area of the stream where rocks couldn’t be seen.
“All this is just mud. It is nothing but mud,” he said. “Nothing's going to use that. And then all of a sudden when you add the flow, we found a pocket of really good gravel that fish will use to spawn.”
The creek channel was already doing what a natural creek should do before construction wrapped up, he said.
“ I think a coho will be spawning in that,” Zacavish said.
Read the audio transcript here.
