The river known for forming the border between the United States and Canada is the St. Lawrence River. This significant waterway flows from the Great Lakes to the Atlantic Ocean, acting as a crucial shipping route. The river is approximately 1,197 kilometers long and serves as an important economic artery for both countries. Its scenic beauty and diverse ecosystems make it a popular destination for recreational activities. Forming a natural boundary, the St. Lawrence River has played a central role in the history and development of both nations.