evidence: The "Courantyne River" forms the international border between which two countries? Notes: The "Courantyne River" forms the international border between Suriname and Guyana. The Courantyne River is a river in northern South America in Suriname. It is the longest river in the country and creates the border between Suriname and the East Berbice-Corentyne region of Guyana. Its tributaries include Kutari River, Coeroeni River, New River, and Zombie Creek. In Suriname, it includes the Kabalebo River, Lucie River, Sipaliwini River, Kutari River.