Trouble ahead for already stressed salmon populations

A number of causes are combining this year to create dangerous conditions for coho salmon. Extreme summer weather, and variability brought about by the ensuing El Niño event are coalescing to contribute to bad news for salmon in the Pacific Northwest. This summer high temperatures and low rainfall produced record high stream temperatures that resulted in massive fish kills (and reduced spawning numbers in smaller streams) in major rivers in the Pacific Northwest. The summer drought led to high intensity of forest fires that swept across Oregon and Washington state. The fires, inhibit the ability of the watershed to slow rainfall, and lead to harmful sedimentation in the rivers and streams. Many folks were welcoming the return of the rainy season to help alleviate the stress of low flows and fires, but be careful what you wish for.


Salmon die when exposed to urban pollutants entering the stream through large rain storms.  Flickr creative commons, photo by Nicole Pezzuti. 

The El Nino this year will produce a drier, warmer winter with the precipitation coming in the form of high intensity rainfall events. We have, in Portland, already seen some of these high intensity rainfall events in late October and early November. These high rainfall events are especially concerning early on in the fall, when soil is drier and unable to soak up the rain as fast as it comes down. The run-off from these storms overwhelms the capacity of green infrastructure to filter harmful contaminants and toxins from urban areas. Many fish such as salmon are negatively affected by the outflow of urban pollution into streams. With all this bad news there seems to be no hope for fish, but scientists are working hard to help alleviate the stress.


Urban storm water drainage pipe dumping fish killing chemicals into streams,


A recent study from scientists at Washington State University and the US Fish and Wildlife service are working on a solution to save the salmon. They found that when adult coho salmon are exposed to highway run-off there is complete mortality within a day. The scientists do not know what exactly it is in the highway run-off that is killing the salmon, but they know it’s not good. They developed a system, composed of a three foot mixture of soil and plant material, which successfully filtered out the toxins from highway. This treatment resulted in storm water that was safe for salmon. This finding shows us that if we implement a little more green technology the world might just be a little safer for salmon, that seem to get into more trouble every day.



Run-off filtration systems removes dangerous toxins to fish,



Cover image

Coho salmon, stressed after high summer temperatures, face further obstacles,


Research Article;

Julann A. Spromberg, David H. Baldwin, Steven E. Damm, Jenifer K. McIntyre, Michael Huff, Catherine A. Sloan, Bernadita F. Anulacion, Jay W. Davis, Nathaniel L. Scholz. Coho salmon spawner mortality in western US urban watersheds: bioinfiltration prevents lethal storm water impacts. Journal of Applied Ecology, 2015; DOI: 10.1111/1365-2664.12534

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