The salmon were dying and nobody knew why.

About 20 years ago, ambitious restoration projects had brought coho salmon back to urban creeks in the Seattle area. But after it rained, the fish would display strange behaviors: listing to one side, rolling over, swimming in circles. Within hours they would die — before spawning, taking the next generation with them. In some streams, up to 90 percent of coho salmon were lost.

Jen Mcintyre.

“To be running into these sick fish was fairly astonishing,” said Jenifer McIntyre, now a toxicologist and professor at Washington State University who is part of a team that, years later, has finally solved the mystery of the dying salmon around Puget Sound. “In those early years, we debated intensely, what could be the cause of this?”

Partnering with a local fish hatchery run by the Suquamish Tribe, they decided to put the theory to the test, exposing fish to a mixture they created of chemicals they knew to be in roadway runoff, like heavy metals and hydrocarbons from motor oil. But the salmon were unaffected, even at surprisingly high concentrations.

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