Panama Canal Zone
The Panama Canal Zone () was an unincorporated territory of the United States from 1903 to 1979, centered on the Panama Canal and surrounded by the Republic of Panama. The zone consisted of the canal and an area generally extending on each side of the centerline, excluding Panama City and Colón, which otherwise would have been partly within the limits of the Zone. Its border spanned three of Panama's provinces. When reservoirs were created to assure a steady supply of water for the locks, those lakes were included within the Zone.
History of the Panama Canal
After construction, the canal and the Canal Zone surrounding it were administered by the United States. On September 7, 1977, US President Jimmy Carter signed the Torrijos-Carter Treaty setting in motion the process of transferring control of the canal to Panama. The treaty became effective on October 1, 1979, providing for a 20-year period in which Panama would have increasing responsibility for canal operations before complete US withdrawal on December 31, 1999. Since then, the canal has been administered by the Panama Canal Authority (Autoridad de Canal de Panama, or ACP).