San Juan (sän hwän), 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.

San Juan (săn wän), river, c.400 mi (640 km) long, rising in the San Juan Mts., SW Colo., and flowing generally W through N.Mex. and Utah to Lake Powell on the Colorado River. Navajo Dam, part of the upper Colorado River storage project, is on the river, which is unnavigable. Its chief tributaries are the Animas, Los Pinos, La Plata, Piedra, and Mancos rivers. The San Juan is used for irrigation; vegetables, fruits, and grains are grown in the river valley in northwestern N.Mex.

San Juan (săn wän, Span. sän hwän), city (1991 pop. 353,476), capital of San Juan prov., W Argentina. It is a commercial and industrial center in an agricultural region. Wine is the chief product, and vineyards dot the picturesque landscape. Fruits and grains are grown, cattle are raised, and the province is rich in minerals. Founded in 1562, San Juan figured prominently in the civil wars of the 19th cent. Many Argentine statesmen, including Domingo Faustino Sarmiento, were born in San Juan.