38°52′32.1″N 7°2′10″W / 38.875583°N 7.03611°W / 38.875583; -7.03611

Caia (Rio Caia)
The Guadiana river basin in the Iberian Peninsula
Location
Country	Spain, Portugal
Physical characteristics
Source
• location	Serra de São Mamede, Portugal
Mouth
• location	Guadiana River, near Badajoz, Spain
Basin size	846 square kilometres (327 sq mi)
Basin features
Progression	Guadiana→ Gulf of Cádiz

The Caia (Portuguese pronunciation: [ˈkajɐ]) is a river in the Iberian Peninsula, a tributary to the Guadiana. It is one of the main water courses in the Portalegre District, Portugal. Portugal does not recognise the border between the Caia and Ribeira de Cuncos River deltas, since the beginning of the 1801 occupation of Olivenza by Spain. This territory, though under de facto Spanish occupation, remains a de jure part of Portugal, consequently no border is henceforth recognised in this area.

Course

It has its sources in the Serra de São Mamede and for the lower 11 kilometres (7 mi) of its course it forms the international Portugal-Spain border. Finally it joins the Guadiana River southwest of the city of Badajoz.

Tributaries

• Arronches, also known as Alegrete
• Algalé

Dams

• Caia Dam, with the largest reservoir of Portalegre District^[1]