A sign warning of PFAS risks in Starkweather Creek in Madison, Wis., is posted along the creek at McCormick Park on July 20, 2021. Starkweather Creek is contaminated with PFAS, a group of human-made "forever chemicals" that accumulate in the body and persist in the environment without fully breaking down. Research has linked the substances to low birth weights, immune system challenges, thyroid problems, certain cancers and more. Isaac Wasserman/Wisconsin Watch