“Certifying agency means the person or agency designated by the Governor of a State, by statute, or by other governmental act, to certify compliance with applicable water quality standards. If an interstate agency has sole authority to so certify for the area within its jurisdiction, such interstate agency shall be the certifying agency. Where a State agency and an interstate agency have concurrent authority to certify, the State agency shall be the certifying agency. Where water quality standards have been promulgated by the Administrator pursuant to Section 303(c)(4) of the Act, or where no State or interstate agency has authority to certify, the Administrator shall be the certifying agency.”
(40CFR121.1(e))