Oral Declarations of Citizenship No Longer Sufficient At Land, Sea POEs
Citizens of the United States, Canada, and Bermuda entering the U.S. at land or sea ports-of-entry (POEs) must establish their identity and citizenship to the satisfaction of a U.S. Customs and Border Protection (CBP) officer. Under current CBP procedures, such individuals may provide any proof of identity and citizenship. Although most individuals provide documentary evidence of citizenship, such as a passport or birth certificate, individuals currently may be admitted on an oral declaration, depending on the circumstances. Effective January 31, 2008, however, all travelers must present documents proving citizenship (such as a birth certificate), and government-issued documents proving identity (such as a driver’s license), when entering the U.S. through land and sea POEs. CBP retains its authority to request additional documentation when warranted and to make appropriate individual exceptions.
More on the requirements here.