The river Dão is a river of Portuguese plateau which rises in the district of Eirado, more specifically in Barranha, Aguiar da Beira municipality, Guarda District, in the Central Highlands region of Trancoso-Aguiar da Beira.

Its course is done in the northeast-southwest direction and, along it, in addition to having the dam Fagilde in your water stream, empties into the Mondego River in full Bayou Aguieira Dam, on the outskirts of Santa Comba municipalities Dão, Mortágua and Penacova, after covering about 92 kilometers. Its main tributaries are the Rio Carapito, Ribeira de Coja, River Sátão, River Pavia, Ribeira das Hortas and River Cris. In its valley, altitude area with granite soil, is located demarcated region of Dão, which stands out the production of excellent table wines.