The river Ocreza rises in Gardunha Mountain, more specifically in the civil parish of São Vicente da Beira, at an altitude of 1160 m. It flows into the Tagus, 12 kilometers from Fratel. It is a periodic river, with several tributary streams, notably the Senhora da Orada, Líria, Pracana, Alvito and Sarzedinha streams; it feeds the Salles Viana (800 m above sea level), the Santa Águeda/Marateca (385 m above sea level) and the Pracana (114 m above sea level) dams, the latter of which produces hydroelectric power.

Between the Pracana dam and Barca da Amieira, dozens of small dotted figures created tens of thousands of years ago in dark stones take us back to Prehistory.