There are some 1,800 rivers in Spain, but many of them are dry most of the year. The Tagus River (Tajo in Spanish, Tejo in Portuguese) is the longest river in the Iberian Peninsula. It has its source in the Fuente Garcia in the Albarracin mountains of Aragon, Spain. The Tagus flows for 626 miles to the Atlantic Ocean at Lisbon, Portugal.
The Tagus is one of five major Spanish rivers. Along with three other rivers -- the Duero, Guadalquiver and Guadiana -- it flows east to west into the Atlantic. Toledo is the only large city located on the Tagus. The dearth of large cities on the river's course within Spain reflects the rugged mountainous terrain and arid soil of the areas through which it flows. The river is navigable only on the Portuguese side, where it supplies Lisbon with its excellent natural harbour.
The conurbations of Greater Madrid and Greater Lisbon, the capitals of Spain and Portugal, respectively, both depend on the Tagus for their water supply, even though Madrid is not located on the river. The River Manzanares flows through Spain's capital city and joins the River Jarama, which is a tributary of the Tagus. The two have their confluence at Aranjuez.
There are a number of large dams along the course of the Spanish (upper) Tagus, providing hydro-electrical power generation as well as water for irrigation. The Alcantara, Valdecanas and Torrejon dams are the largest, all creating major reservoirs. The Alcantara dam, hard by the Portuguese border, is especially important in regulating the flow of the river.
During the dictatorship of General Franco in the late 1960s, several ambitious water transfer projects were initiated for the purpose of using the Tagus to irrigate Spain's arid interior. The result was a lower volume of water and an increase in pollution levels in Spain. These problems also occurred downstream in Portugal, and have led to much friction between the countries over the years. In 1998, Spain and Portugal signed the Albufeira Convention, which is designed to promote cooperation in the regulation of the use of waters that cross their border. This includes the Tagus River.
The Tagus River partly encircles the historic city of Toledo. Situated in the centre of the Iberian Peninsula roughly 43 miles south of Madrid, Toledo has a population of around 75,000. Owing to its beauty, history and the antiquity of its buildings, it is one of the most popular destinations for tourists in Spain. Fun fact: the expression "holy Toledo" may reflect that the city boasts a plethora of religious sites (Christian, Muslim and Jewish) as a result of its diverse multicultural past.