History of the Panama Canal
During World War II, the canal proved a vital part of the U.S. military strategy, allowing ships to transfer easily between the Atlantic and Pacific. Politically, the Canal remained a territory of the United States until 1977, when the Torrijos–Carter Treaties began the process of transferring territorial control of the Panama Canal Zone to Panama, a process completed on 31 December 1999.
Hay–Bunau-Varilla Treaty
The Republic of Panama grants the United States with any lands, buildings, water rights, or other properties necessary for construction or operation and protection of the Canal. This may include any works of sanitation such as the collection and disposition of sewage in said cities of Panama