The
Caia 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.