Oyapock

The Oyapock or Oiapoque River (French: Fleuve Oyapock; Portuguese: Rio Oiapoque) is a 370-km (230-mi) long river in South America that forms most of the border between French Guiana and the Brazilian state of Amapá. It rises in the Tumuk Humak (Portuguese: Tumucumaque) mountain range and flows into the Atlantic Ocean, where its estuary forms a large bay bordering on Cape Orange.