For decades, Coho salmon were turning up dead in urban streams the Pacific Northwest. The salmon would stop swimming straight, and then die before they had a chance to spawn. Researchers worried that unless they figured out the cause, the species would eventually go extinct. Enter a formidable crew of biologists, modelers, community scientists, environmental chemists. After eventually ruling out the obvious suspects — things like temperature, oxygen levels and known toxins — researchers eventually zeroed in on a prime suspect: chemicals in tires. But the question remained: Which one? If you liked this episode, check out our other episodes on satellites monitoring emissions and how air pollution could create superbugs.Want to hear more environmental stories or science mysteries? Tell us by emailing shortwave@npr.org!Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave.Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy