Editing Guadiana (section)

==Watershed==
[[File:Rio guadiana.jpg|thumb|left|Lake Alqueva along the River Guadiana]]
[[File:Alqueva dam.JPG|thumb|left|The [[Alqueva Dam]], located in the southern arm of the Guadiana, is responsible for Western Europe's largest reservoir.]]
The Guadiana flows east to west through Spain and south through Portugal, then forms the Spanish-Portuguese border; it flows into the [[Gulf of Cádiz]], part of the Atlantic Ocean, between [[Vila Real de Santo António Municipality|Vila Real de Santo António]] (Portugal) and [[Ayamonte]] (Spain). It is {{convert|818|km|mi}} long, of which {{convert|578|km|mi}} are within Spanish territory, {{convert|140|km|mi}} within Portugal, while {{convert|100|km|mi}} are shared between the two nations. About 82&nbsp;percent, {{convert|55,444|km2|mi2}}, of its basin is in Spain, while about 17&nbsp;percent, {{convert|11560|km2|mi2}} is in Portugal.{{sfn|Aldaya|Llamas|2009|p=6}}

===Sources===
The exact source of the river  in Castilla-La Mancha is disputed, but it is generally believed to spring in the {{ill|Ojos del Guadiana|es}}, [[Villarrubia de los Ojos]] municipal term, [[Ciudad Real Province]], Castile–La Mancha, about {{convert|608|m|ft}} in elevation.

A classic theory introduced by [[Pliny the Elder]], was that the river originated from the [[Lagunas de Ruidera]] and divided into two branches: the Upper Guadiana ({{langx|es|Guadiana Viejo|links=no}}) and the Guadiana, while separated by a subterranean course. This legend developed from a misguided belief (which persisted until the 19th century) that the river appeared and disappeared over time, because of its subterranean tributary. In fact, no subterranean course exists, and the belief that the Lagunas de Ruidera is the source is also controversial. toponymically and traditionally the Upper Guadiana,<ref>José Díaz-Pintado Carretón, 1997</ref> which runs from [[Viveros]] ([[Albacete]]) until [[Argamasilla de Alba]] ([[Ciudad Real]]) had been identified as the main branch of the Guadiana. But even hydro-geological characteristics indicate that the Upper Guadiana may not be the principal river within the system.<ref>A. Cabo Alonso, 1991</ref>

Another of the origin theories, postulated that the [[Cigüela River|Cigüela]] and [[Zancara River|Záncara]] rivers were the sources of the Guadiana. Today, they are considered integral parts of the river's headwaters and important tributaries, but not necessarily the exact origin. The Ciguela's source is in Altos de Cabreras ([[Cuenca Province (Spain)|Cuenca]]) and pertains to the [[Sistema Ibérico]], at an elevation of {{convert|1080|m|ft}}. Its course is {{convert|225|km|mi}} long, receiving contributions from the rivers Jualón, Torrejón, Riánsares, Amarguillo and [[Záncara]]. The union of the rivers Ciguela and Záncara permits the replenishment of the waters in the [[Tablas de Daimiel National Park]], a wetland that was designated for protection by the Spanish government in 1973 (situated in the municipalities of Villarrubia de los Ojos and [[Daimiel]], in the province of Ciudad Real).

===Course===
From its origin/spring runs from the southern Iberian plain in a direction east to west, to near the town of [[Badajoz]], where it begins to track south leading to the Gulf of Cádiz. The Guadiana marks the border of Spain and Portugal twice as it runs to the ocean: first, between the River [[Caia (river)|Caia]] and [[Ribeira de Cuncos]], then later from the [[Chanza River|River Chança]] until its mouth. The river is not used to completely mark the boundary between the two states; between the Olivenza ravine and the Táliga ravine, the border still remains a disputed section claimed ''[[de jure]]'' by both countries and administered ''[[de facto]]'' by Spain (as part of the Spanish [[Autonomous communities of Spain|autonomous community]] of [[Extremadura]]).

For the most part, the Guadiana is navigable from the Atlantic Ocean until [[Mértola]], a distance of {{convert|68|km|mi}}. North of Mértola on the Guadiana is the highest waterfall is Southern Portugal called [[Pulo do Lobo]].

The ecosystem has Mediterranean hydrological characteristics, including high variation in intra- and inter-annual discharge, large floods and severe droughts. This variability is a consequence of considerable variation in rainwater supply averaging around an annual mean of {{convert|400|to|600|mm|in}}.<ref>Chicharro, et al., 2007, p.109</ref> The climate is [[Semi-arid climate|semiarid]] with an average annual temperature of {{convert|14|to|16|C|F}}.{{sfn|Aldaya|Llamas|2009|p=8}}