Summary: For more than 25 years, urban stormwater runoff has been implicated as a causative factor leading to pre-spawn mortality for coho salmon in the Pacific Northwest. In 2021, academic and federal researchers using high-resolution mass spectroscopy discovered that a single chemical found in urban stormwater runoff can kill juvenile coho salmon at environmentally measurable levels. The chemical in question is 6PPD-quinone (6PPDQ), a transformation product of 6PPD that is used as an anti-degradant for car tires. 6PPD prevents tires from cracking upon reaction with ozone and oxygen thus providing critical safety features for consumers as well as tire longevity. Other members of the Salmonidae family, including rainbow trout and brook trout, are also sensitive to 6PPDQ thus raising additional concerns for aquatic animal health not just for the U.S., but globally. The USGS has been actively involved in assessing the transport and distribution of 6PPDQ, species sensitivity, and potential modes of action for toxicity. Currently, the California Department of Toxic Substance Control (DTSC) plans to list 6PPD as a Priority Product in California’s Safer Consumer Products program—a stance that is supported by the U.S. Tire Manufacturing Association. This presentation will provide an overview on 6PPDQ and how the USGS is involved in solving the problem of 6PPDQ mediated toxicity.