Río San Juan

The San Juan River (Spanish: Río San Juan), also known as El Desaguadero ("the drain"), is a 192-kilometre (119 mi) river that flows east out of Lake Nicaragua into the Caribbean Sea. A large section of the border between Nicaragua and Costa Rica runs on the southern bank of the river. It was part, with the lake, of a proposed route for a Nicaragua Canal in the 19th century. The idea of the project has been revived in the last decade, including the possibility of other routes within the country. The Ecocanal project has obtained a Concession from the National Assembly of Nicaragua to re-open the San Juan River to commercial barge traffic.

The Cañas–Jerez Treaty states that Nicaragua owns the waters of the river and that Costa Rica can only use it for commercial navigation on certain parts of the river at Nicaragua's discretion.