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You're listening to Shortwave from NPR.

Hey, shortwavers, Camila Dominosky here in the host chair with a mystery, a decades-long puzzle, centering on a string of inexplicable deaths.

The victims were co-host salmon, showing up dead in urban streams in Puget Sound around Seattle in very suspicious circumstances.

They show weird symptoms like they're drunk, so they cannot swimming in a straight line.

They're like swimming in circles.

And usually when they show that symptom, they will be dead in like a few hours.

That's Gen Yutien, whom you might call one of the lead detectives on this case.

He was a postdoc research scientist at the Center for Urban Waters at the University of Washington, Tacoma,

when he was called in to the case.

These fish spawn in freshwater, strike off for the open seas, trek back to the

place of their birth, but then they die before they can spawn. And this keeps happening for years.

If this trend continual, they might be, like, extinct in a few decades. So that's the problem we want to solve.

And we was a lot of people, biologists, modelers, community scientists, environmental chemists.

Some researchers rule out all the obvious culprits. Temperature, oxygen, known toxins. It's none of those. They need a lead.

So I think the first big step is our collaborators, NOAA and the Washington State University.

They look through the data about where fish were dying and started running models.

They are getting this important clue that the mortality risk of

Kauka Salmon is related to traffic. Traffic. It's something to do with the roads, the urban

runoff. So after years of work, the list of suspects is narrowing, but what part of the

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