New research shows that stormwater runoff, which flows into waterways when it rains, can kill Coho salmon in as much as 40 percent of their local habitat.

Entitled “Roads to ruin: conservation threats to a sentinel species across an urban gradient,” the paper confirms and broadens earlier conclusions about Puget Sound coho and their vulnerability to pollution from roads in their home range.

The researchers pinpointed the worst areas on a map. That’s meant to help planners get fixes in place quickly otherwise this fish, which is listed as a species of concern under the US Endangered Species Act, could be headed for local extinction.

The grim news is tempered by the fact that relatively easy and inexpensive fixes are available. Past research points to bioretention devices – simple columns of soil, sand, compost and gravel, says Nat Scholz, a research zoologist with NOAA Fisheries’ Northwest Fisheries Science Center and the senior author on the paper. He says channeling the most toxic runoff into these devices neutralizes it.

“Putting it through these experimental columns removes both contaminants that we know about, like metals and petroleum compounds, but also is removing a lot of chemicals that we have yet to identify,” Scholz said.

The State Department of Transportation has been paying attention. Stormwater and Watersheds Program Manager Jana Ratcliff says past research has led to new permitting requirements for highway construction and a stormwater retrofit program. They’re also funding research of their own to improve the tools and techniques available.

“And kind of mesh the research that they’re doing with what can we actually do in the field to get these best management practices in place and start filtering this water,” Ratcliff said.

She says constraints include the narrow right of way that WSDOT has to work with in siting bioretention devices and available state funding.

“But as we go out and build new projects, we are including these best management practices to improve the quality of the rivers and streams that they flow to."

The new paper is published in the journal Ecological Applications.