Scientists Finally Found What's KILLING Seattle's Salmon — And It's NOT What Anyone Expected

Every fall, coho salmon fight their way back from the Pacific to the creeks of Seattle to lay their eggs. For years, most of the females never did. In Longfellow Creek, surveyors found that 60 to 100 percent of them died first, often within one to two hours, still full of eggs. The water was cold enough. There was plenty of oxygen. No disease explained it. So what was killing them? This is the story of a twenty-year search: eight years of counting dead fish, five suspects crossed off one by one, nine storms' worth of highway runoff, two thousand chemicals, and one stubborn idea that finally named the killer. And why it is still out there today. CHAPTERS 0:00 The fish that never spawned 0:23 The creek 2:19 A thousand to one 4:27 Counting the dead 6:55 The usual suspects 9:26 The highway test 11:58 Two thousand chemicals 15:07 On every road 17:35 The fix SOURCES • Tian et al., "A ubiquitous tire rubber–derived chemical induces acute mortality in coho salmon," Science (2020) • Scholz et al., "Recurrent die-offs of adult coho salmon returning to spawn in Puget Sound lowland urban streams," PLoS ONE (2011) • Spromberg et al., "Coho salmon spawner mortality in western US urban watersheds: bioinfiltration prevents lethal storm water impacts," Journal of Applied Ecology (2016) • Feist et al., "Roads to ruin: conservation threats to a sentinel species across an urban gradient," Ecological Applications (2017) • Follow-up studies in Environmental Science & Technology and ES&T Letters (2021–2023) • NOAA Fisheries — coho salmon species profile • U.S. Environmental Protection Agency — response to the tribal petition on 6PPD (2023) and 2024 screening values • University of Washington News and Washington Stormwater Center — tires and salmon research summaries A note on the pictures: some scenes in this video are illustrations made with AI, the talking-fish scenes are our own cut-out animations, and some maps and diagrams are our own graphics. The numbers and events come from the sources above. Would you pay a little more for a set of tires if you knew they were safe for salmon? Tell us in the comments. #salmon #seattle #wildlife