Imagine that every time it rains in the city, something invisible—and deadly for fish—washes off the roads and into the nearest stream. The fish die there within a few hours, and for years no one could figure out why. This is what happened in Seattle for decades. And when scientists finally solved the mystery, it turned out the answer was right under everyone’s feet—more precisely, under the wheels.
Orcas off Seattle’s Coast: Beautiful—and in Danger
In Puget Sound, right off the coast of Seattle, lives a special group of orcas. Scientists call them “Southern Resident Killer Whales.” These aren’t just beautiful animals. For many Indigenous peoples in the region, orcas are sacred beings—symbols of power and wisdom. People here have lived alongside them for centuries, fishing in the same waters.
But today there are very few left—about seventy individuals. That’s dangerously small for a population to stay healthy. For comparison, there are more students in a single school in Moscow than orcas left in the whole world. Scientists have long noticed that these orcas are getting thinner, sick more often, and having fewer calves.
The main reason is lack of food. The orcas eat almost exclusively salmon—especially a large salmon called Chinook. But there are fewer and fewer Chinook salmon in the bay.
And that’s where our detective story begins.
A Mystery Nobody Could Solve
Since the 1990s, biologists have noticed something strange. In fall, when it starts raining in Seattle, coho salmon in city streams suddenly act very differently. The fish swim in circles, lose their balance, roll onto their sides—and then die. Sometimes, within a few hours, most of the fish in a stream would die.
Scientists even gave it a name: the “fall coho salmon die-off syndrome.” It sounds scientific, but really it was just a label for something they couldn’t understand.
They checked everything. Maybe pesticides from farms? No. Heavy metals? Not that either. Diseases? Not likely. The mystery stayed unsolved for almost thirty years. It felt like a detective story where you have all the clues—yet the “criminal” can’t be found.
One thing was clear: the fish died after rain, and it happened in city streams—where rainwater runs off roads. So something was washing off the roads. But what, exactly?
An Old Tire as the Unexpected Villain
In 2020, a team of scientists from the University of Washington finally found an answer. And it was completely surprising.
Car tires contain a special chemical added to help the rubber last longer and resist cracking. It’s called 6PPD. By itself, it isn’t very dangerous. But when a tire rolls on the road and the chemical reacts with air, it turns into another substance—6PPD-quinone. Tiny particles of this chemical land on the asphalt. When it rains, the water carries them away—into storm drains and then into streams and rivers.
And then comes the scary part: even a tiny amount can kill coho salmon within a few hours. Scientists tested it and confirmed that 6PPD-quinone was the invisible killer they had been searching for for nearly thirty years.
This discovery shocked the whole scientific world. Think about it: a chemical found in every tire on every car—on your mom’s car, on the school bus, on trucks—was quietly killing fish every time it rained. And nobody knew.
It’s important to understand: coho salmon is not the fish that orcas mainly eat. Southern Resident orcas prefer Chinook salmon. But this discovery revealed something very important: city roads can poison river life. And when one fish kind suffers, the whole river ecosystem suffers too—and in the end, that can affect orcas, because they depend on a healthy supply of salmon.
How Seattle Changed Because of This Discovery
The news spread around the world. And Seattle— a city that’s often proud of its love for nature—started taking action.
First, scientists and engineers began developing special filters for stormwater. It turned out that ordinary soil—when paired with the right plants—can trap the dangerous chemical. It sticks to particles of earth instead of reaching the stream. These small “filter gardens” are called bioretention cells, or simply rain gardens. They started appearing all over Seattle right alongside roads. They’re not just pretty flower beds: they work like natural cleaning systems.
Second, tire manufacturers faced pressure. Scientists and nature advocates demanded that the harmful chemical be replaced. That is difficult and expensive, but the work has already begun.
Third—and this may be the most important part—the tire story made the whole city think differently about how city life connects with the natural world. People used to say: well, we live in the city, and nature is somewhere else—in the forests or out in the ocean. Now it became clear that every car, every road, every rainstorm is connected to the orcas in the bay. City and nature aren’t two separate worlds. They are one.
Today, Seattle runs special programs to protect orcas. Boats slow down near areas where orcas feed, so engine noise doesn’t make hunting harder. Fishing is regulated so there is enough salmon for both people and orcas. And rain gardens are now part of city design—beautiful and useful at the same time.
One City—One Ecosystem
The story of tires and orcas teaches us something important: in nature, everything is connected. Sometimes the connection is surprising. Who would think that a car tire and an orca in the ocean could be linked?
Seattle is one of the few cities in the world located right by a bay where wild orcas live. That is a huge privilege—and also a huge responsibility. Residents here understand that. In 2018, when an orca named Tahlequah carried her dead calf through the bay for seventeen days—as if she didn’t want to let go—people all over the world cried with her. Those images traveled across news sites everywhere.
Maybe that’s part of why Seattle takes orca protection so seriously. When you see such grief, you realize it’s not just animals. They’re neighbors. And what we do in our city every day affects their lives—whether we mean to or not.
The 2020 discovery showed that even small changes matter. A rain garden by a road. A filter in storm drains. A slower-moving boat. Together, these are small steps toward a Puget Sound where healthy, well-fed orcas can splash again.