Editors' Summary: Water quality standards-based regulation has been the "reserve clause" of the Clean Water Act (CWA), intended to clean up waters that remain polluted after the application of technology standards. For 20 years, these provisions lay idle, prodded forward at least by litigation in the early 1990s. Today, they are at the center of nearly two dozen lawsuits, a Federal Advisory Committee Act committee, and a flurry of regulatory guidance. Their implementation presents serious issues of federalism, science, and political will. In a prior Article in ELR—The Environmental Law Reporter, the author discussed the origin of CWA §303(d), the Act's provision on water quality standards. In this Article, he describes the implementation of §303(d).