The CWA establishes the basis for the water quality standards (WQS) regulation and program. CWA section 303 addresses the development of state and authorized tribal WQS that serve the CWA objective for waters of the United States. The core components of WQS are designated uses, water quality criteria that support the uses, and antidegradation requirements. Designated uses establish the environmental objectives for a water body and water quality criteria define the conditions sufficient to achieve those environmental objectives. The antidegradation requirements provide a framework for maintaining and protecting water quality that has already been achieved. The CWA creates a partnership between states and authorized tribes, and EPA, by assigning states and authorized tribes the primary role of adopting WQS (CWA sections 101(b) and 303), and EPA the oversight role of reviewing and approving or disapproving state and authorized tribal WQS (CWA section 303(c)). Absent state or authorized tribal adoption or submission of new or revised WQS, section 303(c)(4)(B) of the CWA gives EPA the authority to determine that new or revised WQS are necessary to meet the requirements of the Act. Once the Administrator makes such a determination, EPA must promptly propose regulations setting forth new or revised WQS for the waters of the United States involved, and must then promulgate such WQS, unless a state or authorized tribe adopts and EPA approves such WQS first.