The Environmental Protection Agency (EPA) is publishing this final rule to update and clarify the substantive and procedural requirements for water quality certification under Clean Water Act (CWA or the Act) section 401. CWA section 401 is a direct grant of authority to States (and Tribes that have been approved for "treatment as a State" status) to review for compliance with appropriate federal, State, and Tribal water quality requirements any discharge into a water of the United States that may result from a proposed activity that requires a federal license or permit. This final rule is intended to increase the predictability and timeliness of CWA section 401 certification actions by clarifying timeframes for certification, the scope of certification review and conditions, and related certification requirements and procedures.