PUD No. 1 of Jefferson County, Washington (PUD) (plaintiff), a local utility district, proposed to build a new hydroelectric plant on the Dosewallips River, located on federally-owned land. Pursuant to § 404 of the Clean Water Act (CWA), PUD was required to obtain a permit to operate the facility. The State of Washington had stringent and comprehensive water quality standards, approved by the Environmental Protection Agency (EPA), which were intended to prevent degradation of its pristine streams and rivers. Consequently, the Washington Department of Ecology (WDEC) (defendant), permit issued to PUD imposed a variety of conditions, including a minimum stream-flow requirement necessary to protect salmon and trout species thriving in the river. Upon review, a state administrative appeals board concluded the WDEC had exceeded its authority in conditioning the permit issued to PUD. However, a state superior court upheld WDEC’s permit requirements as necessary to protect the fishery. PUD appealed. The Washington Supreme Court affirmed the lower court’s holding and concluded the antidegradation provisions of the State’s water quality standards required imposition of minimum stream flows. The U.S. Supreme Court granted certiorari to resolve a conflict among the state courts regarding the issue.