EPA updates the federal water quality standards (WQS) regulation to provide a better-defined pathway for states and authorized tribes to improve water quality and protect high quality waters. The WQS regulation establishes a strong foundation for water quality management programs, including water quality assessments, impaired waters lists, and total maximum daily loads, as well as water quality-based effluent limits in National Pollutant Discharge Elimination System (NPDES) discharge permits. In this rule, EPA is revising six program areas to improve the WQS regulation's effectiveness, increase transparency, and enhance opportunities for meaningful public engagement at the state, tribal and local levels. Specifically, in this rule EPA: Clarifies what constitutes an Administrator's determination that new or revised WQS are necessary; refines how states and authorized tribes assign and revise designated uses for individual water bodies; revises the triennial review requirements to clarify the role of new or updated Clean Water Act (CWA) section 304(a) criteria recommendations in the development of WQS by states and authorized tribes, and applicable WQS that must be reviewed triennially; establishes stronger antidegradation requirements to enhance protection of high quality waters and promotes public transparency; adds new regulatory provisions to promote the appropriate use of WQS variances; and clarifies that a state or authorized tribe must adopt, and EPA must approve, a permit compliance schedule authorizing provision prior to authorizing the use of schedules of compliance for water quality-based effluent limits (WQBELs) in NPDES permits. In total, these revisions to the WQS regulation enable states and authorized tribes to more effectively address complex water quality challenges, protect existing water quality, and facilitate environmental improvements. The final rule also leads to better understanding and proper use of available CWA tools by promoting transparen