Salmon are also making a resurgence in some areas where storm water runoff is being controlled and filtered. A chemical in tires to prevent cracking is lethal for Chinook and Steelhead, so keeping that out of watersheds could create huge population increases due to the amount of eggs. "6PPD-quinone, that is deadly to coho salmon at extremely low concentrations and is often found in urban streams. Stormwater run-off from roads kills both juvenile and adult coho within a matter of a few hours. Even stormwater diluted to a mixture of just 5 percent highway runoff still killed juvenile coho, the new research found." https://www.fisheries.noaa.gov/feature-story/roadway-runoff-...