AVERY COOPER: Salmon like water temperatures just so. Rivers can't be too hot. But there's one small spot along the lower Yakima River that could help. NWPB's senior environmental correspondent Courtney Flatt has the story.

COURTNEY FLATT: When adult salmon make a left turn into the Yakima River each summer, the water they run into can be too hot to survive in.

Zac Zacavish is a fish research biologist with the Yakama Nation. He says this part of the Yakima is a huge bottleneck for salmon.

ZACAVISH: "In June to July, we have a super hot river. Water's coming down, temperatures are going up."

FLATT: But one creek in the Tri-Cities could help.

Amon Creek is an anomaly on the lower Yakima. Studies show its summertime temperatures run cooler than the main river.

ZACAVISH: “When you have something cold coming into a hot river, the fish are gonna find it, and ideally use it." 

FLATT: Biologists want to enhance Amon Creek's cold water habitat. The work requires rerouting the creek and growing more native plants along the banks.

One of the biggest parts of the project includes building a 70-foot berm that curves out into the Yakima River. That should create a pocket of cool, deep water.

Marcella Appel is the Benton Conservation District manager. 

APPEL: "We are creating, essentially, rest stops for (salmon) as they are migrating. Our hope is that the cold water refuge can increase some of our summer run populations."

FLATT: This is 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.

Before this construction, Amon Creek used to run straight and narrow. 

ZACAVISH: " When you think of degradation, it didn't happen overnight. A lot of things 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."

FLATT: Now, dirt and rock are piled around the construction zone. Crews have capped the old stream so that the water reroutes to a longer, meandering path. 

Adding bends back into a waterway can provide more habitat and reduce erosion. Streams in Washington and Oregon have created better fish habitat after these sorts of projects.

But that's not all they're doing. The berm they're building is a big part of the Amon Creek upgrade. Engineers used a similar berm design on the Pend Oreille River in 20-22. Both rivers are tributaries of the Columbia River and contain important fish habitat. Years later, thermal imaging along the Pend Oreille shows cool water habitat has increased.

In a way, Appel says, the Pend Oreille project was a proof of concept for Amon Creek.

APPEL: "We wanted to see: could we actually bring this and make it?"

FLATT: Engineers learned some lessons during their work on the Pend Oreille River that are helping with the Amon Creek design. They monitored the earlier design and decided to add in more wood and cover where the fish seem to hang out. 

Back at Amon Creek, Appel says the area will require maintenance and upkeep in the future. They plan to monitor and see if salmon are using the new habitat.

And to her surprise, Amon Creek has already naturally unveiled spawning habitat. River rocks glisten at the bottom of the rerouted creekbed.

APPEL: "Oh, they're beautiful."
FLATT: " So what, what looks nice to y'all about this?"
ZACAVISH: "Yeah, why are we all so excited?"

FLATT: Zacavish walks to another section of the stream that doesn't look as healthy.

ZACAVISH: This is nothing but mud. 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."

FLATT: He says, even amid construction, the creek channel is already doing what a natural creek should do.

I'm Courtney Flatt on the banks of a new Amon Creek.

COOPER: This story is part of NWPB's efforts to report not just on problems, but on how our communities are seeking solutions.