Lempa River, El Salvador.
The Lempa River is a 422 km long river in Central America. Its sources are located in between the Sierra Madre and the Sierra del Merendón in southern Guatemala, near the town of Olopa. In Guatemala the river is called Río Olopa and flows southwards for 30.4 km before entering Honduras and changing its name to Lempa river at 14°32′52″N 89°15′50″W / 14.547700°N 89.264002°W / 14.547700; -89.264002. In Honduras it flows through Ocotepeque Department for 31.4 km, and crosses the border with El Salvador at the town of Citalá (14°22′19″N 89°12′45″W / 14.371857°N 89.212439°W / 14.371857; -89.212439) in the department of Chalatenango. The river continues its course for another 360 km in El Salvador, flowing in a generally southwards direction until it reaches the Pacific Ocean in the department of San Vicente.
The river's watershed has an extension 17,790 km², of which 10,082 km2 (56%) is situated in El Salvador, 5,251 km2 in Honduras and 2,457 km2 in Guatemala. 77.5% of the Salvadoran population lives in cities, towns, and villages that are located in the Lempa river basin, including the capital city of San Salvador.