The Barragem de Odelouca, completed in 2012, is the Algarve's main strategic water supply — a large body of still water sitting in a valley that used to be dry scrubland. The reservoir itself is fine to look at, but the reason to come is what lives in the surrounding hills: Bonelli's eagles nest in the rocky outcrops above the waterline, Egyptian vultures pass through in spring and autumn, and the cork oak slopes support one of Portugal's few remaining populations of Iberian azure-winged magpies — a bird that looks improbable, all powder blue and cinnamon, and is genuinely worth seeing. In winter, waterfowl gather on the open water.
The best access is from the road between Silves and São Bartolomeu de Messines. There is no visitor infrastructure — no hides, no trail markers, no café — so bring binoculars, a field guide, and enough water. The birding is best in early morning, when the raptors start working the thermals above the ridge.