Fonseca, Gulf of (fōnsāˈkä) [key], inlet of the Pacific Ocean, c.700 sq mi (1,810 sq km), c.50 mi (80 km) long and c.30 mi (50 km) wide, W Central America. In a volcanic area, it is a natural shallow harbor shared by Nicaragua, Honduras, and El Salvador. It receives the Choluteca River, among others. La Unión, in El Salvador, and Henecán, in Honduras, are the chief ports. Nicaragua leased (1916) a site for a naval base on the gulf to the United States as an adjunct of the Nicaragua Canal, causing protests from El Salvador. Upheld by the Central American Court of Justice, the protests were ignored by the United States and Nicaragua. The first European to explore (1522) the gulf was Gil González de Ávila, a Spaniard.