San Juan (sän hwän) [key], river, c.110 mi (180 km) long, flowing from the southeast corner of Lake Nicaragua E to the Caribbean Sea, near the port of San Juan del Norte. The lower course of the deep navigable river is the boundary between Nicaragua and Costa Rica but belongs to Nicaragua, and Costa Rica's long-affirmed right to free navigation on the river there has been the source of dispute and tension between the two nations. A 2009 International Court of Justice (ICJ) ruling on the issue upheld Nicaragua's right to regulate river traffic while placing limits on what rules it could impose. In 2010, however, tensions flared over a disputed island at the river's mouth when Nicaragua stationed troops there; the troops remained despite a call by the Organization of American States for both sides to withdraw. A 2011 ICJ interim ruling called on both sides to avoid the disputed island.